High-efficiency high-quality and safe alkaline cupric chloride etchant for printed circuit board

Abstract

A high-efficiency high-quality and safe alkaline cupric chloride etchant for printed circuit board, which includes cupric chloride and a sub-etchant. The sub-etchant contains (in percentage by weight) 10%-30% NH4Cl; 0.0002%-25% carboxylic acid and/or ammonium carboxylate; 0.3%-25% ammonium hydroxide. The etchant is used in connection with an automatic detection and charging control during the etching process in order to keep the concentration of copper ions in the etchant no less than a set value.

Claims

1. A high-efficiency high-quality and safe alkaline cupric chloride etchant for printed circuit board, comprising cupric chloride and a sub-etchant, which comprises a temporary storage for ammonium ions during an etching process and said temporary storage is in the form of a reversible reaction as follows:
RCOOH+NH.sub.4OH<=>RCOONH.sub.4+H.sub.2O.

2. The high-efficiency high-quality and safe alkaline cupric chloride etchant for printed circuit board according to claim 1, wherein the sub-etchant comprises the following components in percentage by weight: 15%-30% NH.sub.4Cl; 0.81%-12.7% carboxylic acid and/or ammonium carboxylate; 0.5%-25% ammonium hydroxide; and the balance of water.

3. The high-efficiency high-quality and safe alkaline cupric chloride etchant for printed circuit board according to claim 2, wherein the sub-etchant comprises the following components in percentage by weight: 15%-25% NH.sub.4Cl; 1%-8.5% carboxylic acid and/or ammonium carboxylate; 0.6%-20% ammonium hydroxide; and the balance of water.

4. The high-efficiency high-quality and safe alkaline cupric chloride etchant for printed circuit board according to any one of claim 1, wherein the concentration of copper ions is 60-140 g/L, and the pH value is 7.0-8.0.

5. The high-efficiency high-quality and safe alkaline cupric chloride etchant for printed circuit board according to claim 4, wherein the carboxylic acid is one or more compounds selected from the group consisting of formic acid, citric acid and malic acid; the ammonium carboxylate is one or more compounds selected from the group consisting of ammonium formate, ammonium citrate and ammonium malate.

6. The high-efficiency high-quality and safe alkaline cupric chloride etchant for printed circuit board according to claim 5, wherein an automatic detection and charging control machine is used for additionally controlling the pH process parameter of the etchant during the etching process, so that the pH of the etchant is always within a set numerical range.

7. The high-efficiency high-quality and safe alkaline cupric chloride etchant for printed circuit board according to any one of claim 1, wherein the automatic detection and charging control machine is used for additionally controlling the pH process parameter of the etchant during etching process, so that the pH of the etchant is always within the set numerical range.

8. The high-efficiency high-quality and safe alkaline cupric chloride etchant for printed circuit board according to claim 7, wherein after the cupric chloride at an amount of not less than 1 g/L is pre-added, copper is selected and added instead of cupric chloride into the sub-etchant, and the initial amount C of copper added instead of cupric chloride into the sub-etchant=(set value of the concentration of copper ions A)((pre-charging amount of cupric chloride B)63.5134.5) g/L.

9. A process of utilising the alkaline cupric chloride etchant according to any one of claim 1 for an etching operation, employing an automatic detection and charging control machine with a specific density control system to control the amount of each component in the etchant, characterised in that an automatic detection and charging system for ammonium hydroxide is added onto the automatic detection and charging control machine, in order to monitor the pH value of the etchant in real time; the etchant is subdivided into the following three components; the three components are respectively placed in a corresponding supplement tank, so that each of the components is charged by the automatic detection and charging control machine according to changes of its corresponding process parameters during the etching process: (1) sub-etchant: a mixture of aqueous solutions of ammonium chloride, carboxylic acid and/or ammonium carboxylate, and ammonium hydroxide; (2) ammonium hydroxide as a separate component, so that the said ammonium hydroxide is added as required during the real-time monitoring of the pH of the etchant; (3) cupric chloride; said process comprising the steps of: Step 1 preparing the sub-etchant: at ambient temperature and pressure, according to designated components of the sub-etchant and their mixing ratio, selected raw materials are dissolved in water to prepare the sub-etchant; Step 2 calculating the initial charging amount of the cupric chloride: the cupric chloride is added into the sub-etchant obtained in step 1 according to a set value of the concentration of copper ions; the initial charging amount B of the cupric chloride is calculated according to the following formula:
B=(134.5/63.5)set value A of the concentration of copper ions; Step 3 Setting up specific density and pH value detection: the solution obtained in step 2 is poured into an etchant tank on a printed circuit board production line, and sensor probes of the specific density control system and the automatic detection and charging system for ammonium hydroxide are immersed into the etchant, in order to detect and control the specific density and the pH value of the etchant; Step 4 Replenishing the supplement tanks: the sub-etchant prepared in step 1 is poured into the sub-etchant supplement tank; the sub-etchant supplement tank is connected to the specific density control system; the ammonium hydroxide is poured into the ammonium hydroxide supplement tank; the ammonium hydroxide tank is connected to the automatic detection and charging system for ammonium hydroxide; Step 5 Setting the process parameters: the temperature of the etchant tank is set to 45-50 C., the pressure of spray nozzles of the automatic detection and charging control machine is set to 2-3 kg/cm2, charging control point of the specific density control system is set according to the reading of a hydrometer in the specific density control system of the automatic detection and charging control machine, and pH charging control point of the automatic detection and charging system for ammonium hydroxide is set according to a prescribed pH value; the automatic detection and charging control machine is started and the alkaline cupric chloride etchant is prepared; Step 6 Conducting the etching operation: the etching operation is started; the various process parameters are measured by the automatic detection and charging control machine during the etching operation; the machine automatically controls the supplementation of the various components of the etchant, thereby balancing the amount of each component in the etchant.

10. A process of utilising the alkaline cupric chloride etchant according to claim 4 for an etching operation, employing an automatic detection and charging control machine with a specific density control system to control the amount of each component in the etchant, characterised in that an automatic detection and charging system for ammonium hydroxide is added onto the automatic detection and charging control machine, in order to monitor the pH value of the etchant in real time; the etchant is subdivided into the following three components, the three components are respectively placed in a corresponding supplement tank, so that each of the components is charged by the automatic detection and charging control machine according to changes of its corresponding process parameters during the etching process: (4) sub-etchant: a mixture of aqueous solutions of ammonium chloride, carboxylic acid and/or ammonium carboxylate, and ammonium hydroxide; (5) ammonium hydroxide as a separate component, so that the said ammonium hydroxide is added as required during the real-time monitoring of the pH of the etchant; (6) cupric chloride; said process comprising the steps of: Step 1 preparing the sub-etchant: at ambient temperature and pressure, according to designated components of the sub-etchant and their mixing ratio, selected raw materials are dissolved in water to prepare the sub-etchant; Step 2 calculating the initial charging amount of the cupric chloride: the cupric chloride is added into the sub-etchant obtained in step 1 according to a set value of the concentration of copper ions; the initial charging amount B of the cupric chloride is calculated according to the following formula:
B=(134.5/63.5)set value A of the concentration of copper ions; Step 3 Setting up specific density and pH value detection: the solution obtained in step 2 is poured into an etchant tank on a printed circuit board production line, and sensor probes of the specific density control system and the automatic detection and charging system for ammonium hydroxide are immersed into the etchant, in order to detect and control the specific density and the pH value of the etchant; Step 4 Replenishing the supplement tanks: the sub-etchant prepared in step 1 is poured into the sub-etchant supplement tank, the sub-etchant supplement tank is connected to the specific density control system; the ammonium hydroxide is poured into the ammonium hydroxide supplement tank, the ammonium hydroxide supplement tank is connected to the automatic detection and charging system for ammonium hydroxide; Step 5 Setting the process parameters: the temperature of the etchant tank is set to 45-50 C., the pressure of spray nozzles of the automatic detection and charging control machine is set to 2-3 kg/cm2, charging control point of the specific density control system is set according to the reading of a hydrometer in the specific density control system of the automatic detection and charging control machine, and pH charging control point of the automatic detection and charging system for ammonium hydroxide is set according to a prescribed pH value; the automatic detection and charging control machine is started and the alkaline cupric chloride etchant is prepared; Step 6 Conducting the etching operation: the etching operation is started; the various process parameters are measured by the automatic detection and charging control machine during the etching operation; the machine automatically controls the supplementation of the various components of the etchant, thereby balancing the amount of each component in the etchant.

11. A process of utilising the alkaline cupric chloride etchant for an etching operation according to claim 9 or 10, characterised in that the concentration of the ammonium hydroxide as a separate component is 15%-25%.

12. The high-efficiency high-quality and safe alkaline cupric chloride etchant for printed circuit board according to any one of claim 2, characterised in that the concentration of copper ions is 60-140 g/L, the pH value is 7.0-8.0.

13. The high-efficiency high-quality and safe alkaline cupric chloride etchant for printed circuit board according to any one of claim 3, characterised in that the concentration of copper ions is 60-140 g/L, the pH value is 7.0-8.0.

14. The high-efficiency high-quality and safe alkaline cupric chloride etchant for printed circuit board according to any one of claim 2, characterised in that the automatic detection and charging control machine is used for additionally controlling the pH process parameter of the etchant during etching process, so that the pH of the etchant is always within the set numerical range.

15. The high-efficiency high-quality and safe alkaline cupric chloride etchant for printed circuit board according to any one of claim 3, characterised in that the automatic detection and charging control machine is used for additionally controlling the pH process parameter of the etchant during etching process, so that the pH of the etchant is always within the set numerical range.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) The invention is further described by the following exemplary embodiments. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. Nonessential modification and adjustments made by other people according to the invention still belong to the protection scope of the invention.

(2) In the following exemplary embodiments and comparative examples, the ammonium chloride used is preferably ammonium chloride produced by Guangzhou Chemical Reagent Factory; the formic acid used is preferably formic acid produced by Guangzhou Chemical Reagent Factory; the ammonium formate used is preferably ammonium formate produced by Guangzhou Chemical Reagent Factory; the ammonium hydroxide used is preferably ammonium hydroxide produced by Guangzhou Chemical Reagent Factory; the cupric chloride used is preferably CuCl.sub.2.2H.sub.2O (99.0%) produced by Guangzhou Chemical Reagent Factory; the copper used is preferably copper powder produced by Guangzhou Chemical Reagent Factory; the hydrochloric acid used is preferably 36.5% hydrochloric acid solution produced by Guangzhou Chemical Reagent Factory; the citric acid used is preferably citric acid produced by Guangzhou Chemical Reagent Factory; the malic acid used is preferably DL-malic acid produced by Guangzhou Chemical Reagent Factory; the ammonium citrate used is preferably ammonium citrate produced by Guangzhou Chemical Reagent Factory; the ammonium malate used is preferably ammonium malate produced by Xi'an Dafengshou Biotech Co., Ltd. The automatic detection and charging control machines used are preferably Yegao PCB alkaline etching automatic charging control machine type-2 for the alkaline cupric chloride etching systems and Yegao PCB acidic etching automatic charging control machine type-2 for the acidic cupric chloride etching systems, both of which are produced by Guangzhou Yegao Chemical Co., Ltd. In addition to the above-listed products, those of skill in the art can also select products and equipments with similar properties to those listed herein according to conventional choices to achieve the object of the current invention.

Embodiment 1

(3) Binary control system was employed in the embodiment to control the amount of each component in the etchant.

(4) Step 1: at ambient temperature and pressure, according to the designated components as illustrated in Table 1 below, selected raw materials are dissolved in water to prepare the sub-etchant; 25% ammonium hydroxide was prepared.

(5) Step 2: cupric chloride was added into per liter of the sub-etchant obtained in step 1; the added amount of cupric chloride was obtained by calculation according to the set value of the concentration of copper ions in the solution listed in Table 1:

(6) $\begin{array}{cc}\frac{\mathrm{molar}\mathrm{mass}\mathrm{of}{\mathrm{CuCl}}_2}{\mathrm{molar}\mathrm{mass}\mathrm{of}\mathrm{copper}\mathrm{ion}}=\frac{\begin{array}{c}\mathrm{mass}\mathrm{of}{\mathrm{CuCl}}_2\mathrm{to}\mathrm{be}\mathrm{added}\\ \mathrm{per}\mathrm{liter}\mathrm{of}\mathrm{sub}\text{-}\mathrm{etchant}\end{array}}{\begin{array}{c}\mathrm{mass}\mathrm{of}\mathrm{copper}\mathrm{ion}\mathrm{to}\mathrm{be}\\ \mathrm{added}\mathrm{per}\mathrm{liter}\mathrm{of}\mathrm{sub}\text{-}\mathrm{etchant}\end{array}}=\frac{\mathrm{mass}\mathrm{of}\mathrm{pre}\text{-}\mathrm{added}{\mathrm{CuCl}}_2}{\begin{array}{c}\mathrm{mass}\mathrm{of}\mathrm{copper}\mathrm{ions}\\ \mathrm{corresponding}\mathrm{to}{\mathrm{CuCl}}_2\mathrm{pre}\text{-}\mathrm{added}\end{array}}& \left(\mathrm{Formula}1\right)\end{array}$

(7) Wherein the molar mass of cupric chloride is 134.5 g/mol; and the molar mass of copper ion is 63.5 g/mol. The mass of copper ion to be added into per liter of sub-etchant is 130 g according to the value specified in embodiment 1 of Table 1. Therefore, the mass B of cupric chloride to be added into per liter of sub-etchant is 134.513063.5=275.4 g.

(8) Step 3: the solution obtained in step 2 was poured into an etchant tank, and sensor probes of the automatic detection and charging control machine were immersed into the etchant in order to detect and control various process parameters.

(9) Step 4: the 25% of ammonium hydroxide obtained in step 1 was poured into an ammonium hydroxide supplement tank, which was connected to a charging pump controlled by a pH numerical control meter of the automatic detection and charging control machine; the sub-etchant obtained in step 1 was poured into a sub-etchant supplement tank, which was connected to a charging pump controlled by a specific density numerical control meter of the automatic detection and charging control machine.

(10) Step 5: the temperature of the etchant tank was set to 50 C., the pressure of spray nozzles of the automatic detection and charging control machine was set to 2 kg/cm.sup.2, and the pH value was set as the value specified in Table 1. The automatic detection and charging control machine was started and the etchant was prepared; when the pH of the etchant arrived at the set numerical value, the numerical value of the specific density numerical control meter was set according to the reading of a hydrometer on the automatic detection and charging control machine.

(11) Step 6: the etching operation was started. All the components in the etchant were automatically charged and balanced by the automatic detection and charging control machine, keeping the pH value and the specific density at the numerical values specified.

(12) An etch factor test was carried out using PCBs with size of 620540 mm, copper foil thickness of 1 oz, line width and line spacing of 50.8 m. A pure copper etching rate test board with size of 500300 mm1.5 mm was employed for spray corrosion testing. The etching rate and etch factor K were calculated using methods known in the art, e.g., those described in Printed Circuit Technique by Li Xueming, Occupational Skill Testing Authority of Electronic Industry of Ministry of Industry and Information Technology, fifth edition, p 387-389; Theory and Application of Metal Corrosion, Wei Baoming, Chemical Industry Press, p 5-7; Discussion in Methods of Etch Factor Calculation, Tian Ling, et al., printed circuit information, 2007 No. 12, p 55-56. The calculated results of etching rate and etch factor K are presented in able 2.

Embodiments 2-3

(13) The procedures of embodiment 1 were repeated respectively, using the designated content of each component and parameters of the automatic detection and charging control machine as specified in embodiments 2-3 of Table 1 below. Wherein in step 2, 2 g of cupric chloride was first added into per liter of the sub-etchant obtained in step 1, and then copper was added to allow the concentration of copper ions in the obtained solution to reach the value specified in embodiments 2-3 of Table 1 (i.e. 130 g/L). According to formula 1 and formula 2 described in the background of the invention, the mass of copper added was 130(263.5134.5)=129 g.

Embodiments 4-10

(14) The procedures of embodiment 1 were repeated respectively, using the designated content of each component and parameters of the automatic detection and charging control machine as specified in embodiments 4-10 of Table 1 below. Wherein in step 2, 254.2 g of cupric chloride was added into per liter of the sub-etchant obtained in step 1 to allow the concentration of copper ions in the obtained solution to reach the value specified in embodiments 4-10 of Table 1.

(15) In embodiments 4-10, the composition of the sub-etchant, the concentration of copper ions, and the specific density of the automatic detection and charging control machine are identical but the pH values are different. It is shown from the results that as the pH of the etchant increases, the etching rate increases.

Embodiment 11

(16) The procedures of embodiment 1 were repeated respectively, using the designated content of each component and parameters of the automatic detection and charging control machine as specified in embodiment 11 of Table 1 below.

Embodiment 12

(17) The procedures of embodiment 1 were repeated respectively, using the designated content of each component and parameters of the automatic detection and charging control machine as specified in embodiment 12 of Table 1 below, where in step 1, the concentration of ammonium hydroxide prepared was 15%; in step 2, 63.5 g of cupric chloride was added into per liter of the sub-etchant obtained in step 1 to allow the concentration of copper ions in the obtained solution to reach the value specified in embodiment 12 of Table 1.

Embodiment 13

(18) The procedures of embodiment 1 were repeated respectively, using the designated content of each component and parameters of the automatic detection and charging control machine as specified in embodiment 13 of Table 1 below, wherein in step 1, the concentration of ammonium hydroxide prepared was 15%; in step 2, 127.1 g of cupric chloride was added into per liter of the sub-etchant obtained in step 1 to allow the concentration of copper ions in the obtained solution to reach the value specified in embodiment 13 of Table 1.

Embodiment 14

(19) The procedures of embodiment 1 were repeated respectively, using the designated content of each component and parameters of the automatic detection and charging control machine as specified in embodiment 14 of Table 1 below, wherein in step 1, the concentration of ammonium hydroxide prepared was 20%; in step 2, 190.6 g of cupric chloride was added into per liter of the sub-etchant obtained in step 1 to allow the concentration of copper ions in the obtained solution to reach the value specified in embodiment 14 of Table 1.

Embodiment 15

(20) The procedures of embodiment 1 were repeated respectively, using the designated content of each component and parameters of the automatic detection and charging control machine as specified in embodiment 15 of Table 1 below, wherein in step 1, the concentration of ammonium hydroxide prepared was 20%; in step 2, 241.5 g of cupric chloride was added into per liter of the sub-etchant obtained in step 1 to allow the concentration of copper ions in the obtained solution to reach the value specified in embodiment 15 of Table 1.

(21) In embodiments 12-15, the composition of the sub-etchant and the pH parameter of the automatic detection and charging control machine are the same, but the concentration of copper ions are different. From the results, it can be shown that the etching rate increases with increased concentration of copper ions. However, when the concentration of copper ions is too high (e.g. embodiment 15), the etching rate is relatively low due to the etchant being oversaturated.

Embodiment 16

(22) The procedures of embodiment 1 were repeated respectively, using the designated content of each component and parameters of the automatic detection and charging control machine as specified in embodiment 16 of Table 1 below, wherein in step 2, 296.5 g of cupric chloride was added into per liter of the sub-etchant obtained in step 1 to allow the concentration of copper ions in the obtained solution to reach the value specified in embodiment 16 of Table 1.

Embodiment 17

(23) The procedures of embodiment 1 were repeated respectively, using the designated content of each component and parameters of the automatic detection and charging control machine as specified in embodiment 17 of Table 1 below, wherein in step 2, 360.1 g of cupric chloride was added into per liter of the sub-etchant obtained in step 1 to allow the concentration of copper ions in the obtained solution to reach the value specified in embodiment 17 of Table 1.

Embodiment 18

(24) Unitary control system was employed in the embodiment to control the amount of each component in the etchant.

(25) Step 1: at ambient temperature and pressure, according to the designated components as listed in Table 1 below, selected raw materials are dissolved in water to prepare the sub-etchant.

(26) Step 2: 254.2 g of cupric chloride was added into per liter of the sub-etchant obtained in step 1 to allow the concentration of copper ions in the obtained solution to reach the value specified in embodiment 18 of Table 1; the added amount of cupric chloride was obtained by calculation using formula 1 as described in the background section.

(27) Step 3: the solution obtained in step 2 was poured into an etchant tank, and sensor probes of the automatic detection and charging control machine were immersed into the etchant in order to detect and control various parameters.

(28) Step 4: the sub-etchant obtained in step 1 was poured into a sub-etchant tank, which was connected to the charging pump controlled by a specific density numerical control meter of the automatic detection and charging control machine; the temperature of the etchant tank was set to 50 C., the pressure of spray nozzles of the etching machine was set to 2 kg/cm.sup.2.

(29) Step 5: the pH value of the etchant was measured using a pH meter on the automatic detection and charging control machine, and ammonium hydroxide or water was appropriately supplemented until the pH value arrived at the set value; the numerical value of the specific density numerical control meter was set according to the reading of a hydrometer on the automatic detection and charging control machine; the automatic detection and charging control machine was started.

(30) Step 6: the etching operation was started. The sub-etchant was automatically charged and all the components in the etchant were supplemented and balanced by the automatic detection and charging control machine, keeping the specific density of the etchant at the numerical values specified in Table 1.

(31) An etch factor test was carried out using PCBs with size of 620540 mm, copper foil thickness of 1 oz, line width and line spacing of 50.8 m. A pure copper etching rate test board with size of 500300 mm1.5 mm was employed for spray corrosion testing. The etching rate and etch factor K were calculated using methods known in the art. The automatic detection and charging control machine would automatically recharge and balance each component in the etchant, keeping the specific density at the numerical values specified in Table 1. The calculated results of etching rate and etch factor K are recorded in Table 2.

Embodiments 19-23

(32) The procedures of embodiment 1 were repeated respectively, using the designated content of each component and parameters of the automatic detection and charging control machine as specified in embodiments 19-23 of Table 1 below, wherein in step 2, 254.2 g of cupric chloride was added into per liter of the sub-etchant obtained in step 1 to allow the concentration of copper ions in the obtained solution to reach the value specified in embodiments 19-23 of Table 1.

(33) In embodiments 20-23, the concentration of copper ions and the pH parameter of the automatic detection and charging control machine are set to be the same, but the concentration of carboxylic acid in the sub-etchant are different. From the results, it can be seen that the etching rate increases as concentration of carboxylic acid increases when the concentration of carboxylic acid is relatively low. However, when the concentration of carboxylic acid is high, its effect on increasing etching rate decreases as the solution is relatively saturated.

Embodiment 24

(34) The procedures of embodiment 1 were repeated respectively, using the designated content of each component and parameters of the automatic detection and charging control machine as specified in embodiment 24 of Table 1 below, wherein in step 1, the concentration of ammonium hydroxide prepared was 20%; in step 2, 127.1 g of cupric chloride was added into per liter of the sub-etchant obtained in step 1 to allow the concentration of copper ions in the obtained solution to reach the value specified in embodiment 24 of Table 1.

Embodiments 25-27

(35) The procedures of embodiment 1 were repeated respectively, using the designated content of each component and parameters of the automatic detection and charging control machine as specified in embodiments 25-27 of Table 1 below. Wherein in step 1, the concentration of ammonium hydroxide prepared was 20%; in step 2, 169.4 g of cupric chloride was added into per liter of the sub-etchant obtained in step 1 to allow the concentration of copper ions in the obtained solution to reach the value specified in embodiments 25-27 of Table 1.

(36) In embodiments 25-27, the concentration of carboxylic acid and the concentration of ammonium hydroxide in the sub-etchant are the same, as well as the concentration of copper ions and the pH value of the etchant. However, the concentration of ammonium chloride in the sub-etchant is different. From the results, it can be seen that the etching rate increases with increasing concentration of ammonium chloride, as ammonium chloride takes part in the regeneration reaction of copper(II) ammonia complex.

Embodiments 28-30

(37) The procedures of embodiment 1 were repeated respectively, using the designated content of each component and parameters of the automatic detection and charging control machine as specified in embodiments 28-30 of Table 1 below, wherein in step 2, 254.2 g of cupric chloride was added into per liter of the sub-etchant obtained in step 1 to allow the concentration of copper ions in the obtained solution to reach the value specified in embodiments 28-30 of Table 1.

Comparative Example 1

(38) Step 1: at ambient temperature and pressure, according to the designated components as listed in Table 1 below, selected raw materials are dissolved in water to prepare the sub-etchant.

(39) Step 2: 275.4 g of cupric chloride was added into per liter of the sub-etchant obtained in step 1 to allow the concentration of copper ions in the obtained solution to reach the value specified in comparative example 1 of Table 1; the added amount of cupric chloride was obtained by calculation using formula 1.

(40) Step 3: the solution obtained in step 2 was poured into an etchant tank, and sensor probes of the automatic detection and charging control machine were immersed into the etchant in order to detect and control various parameters.

(41) Step 4: the sub-etchant obtained in step 1 was poured into a sub-etchant tank, which was connected to the charging pump controlled by a specific density numerical control meter of the automatic detection and charging control machine; the temperature of the etchant tank was set to 50 C., the pressure of spray nozzles of the etching machine was set as 2 kg/cm.sup.2.

(42) Step 5: the pH value of the etchant was measured using the pH meter on the automatic detection and charging control machine, and ammonium hydroxide or water was appropriately supplemented until the pH value arrived at the set value; the numerical value of the specific density numerical control meter was set according to the reading of a hydrometer on the automatic detection and charging control machine; the automatic detection and charging control machine was started.

(43) Step 6: the etching operation was started. The sub-etchant was automatically charged and all the components in the etchant were balanced by the automatic detection and charging control machine, keeping the specific density at the numerical values specified in Table 1.

(44) An etch factor test was carried out using PCBs with size of 620540 mm, copper foil thickness of 1 oz, line width and line spacing of 50.8 m. A pure copper etching rate test board with size of 500300 mm1.5 mm was employed for spray corrosion testing. The etching rate and etch factor K were calculated using methods known in the art. The automatic detection and charging control machine would automatically recharge and balance each component in the etchant, keeping the specific density at the numerical values specified in Table 1. The calculated results of etching rate and etch factor K are recorded in Table 2.

Comparative Examples 2-4

(45) The procedures of comparative example 1 were repeated respectively, using the designated content of each component and parameters of the automatic detection and charging control machine as specified in comparative examples 2-4 of Table 1 below wherein in step 2, 254.2 g of cupric chloride was added into per liter of the sub-etchant obtained in step 1 to allow the concentration of copper ions in the obtained solution to reach the value specified in comparative examples 2-4 of Table 1.

Comparative Example 5

(46) Step 1: at ambient temperature and pressure, 31 wt % of HCl was dissolved in water to prepare a sub-etchant; H.sub.2O.sub.2 was used as an oxidant, and was prepared into a solution of 27.5% H.sub.2O.sub.2.

(47) Step 2: 254.2 g of cupric chloride was added into per liter of the sub-etchant obtained in step 1 to allow the concentration of copper ions in the obtained solution to arrive at 120 g/L. The mass of cupric chloride added was calculated according to formula 1 in the background section.

(48) Step 3: the solution obtained in step 2 was poured into an etchant tank, and sensor probes of the automatic detection and charging control machine were immersed into the etchant in order to detect and control various parameters.

(49) step 4: the oxidant (27.5% H.sub.2O.sub.2) was poured into an oxidant tank, which was connected to a charging pump controlled by an ORP numerical control meter of the automatic detection and charging control machine; the sub-etchant was poured into a sub-etchant tank, which was connected to a charging pump controlled by a dissociated hydrogen ion concentration meter of the automatic detection and charging control machine; water was poured into a water tank which was connected to a charging pump controlled by a specific density numerical control meter of the automatic detection and charging control machine.

(50) Step 5: the temperature of the etchant tank was set to 49 C., the pressure of spray nozzles of the etching machine was set to 2 kg/cm.sup.2, the concentration of dissociated hydrogen ions was set to 3.0M, and the oxidation-reduction potential (ORP) was set to 54 mV. The automatic detection and charging control machine was started and the etchant was prepared; when the concentration of dissociated hydrogen ions and the ORP in the etchant arrived at the set numerical values, the numerical value of the specific density numerical control meter was set according to the reading of a hydrometer on the automatic detection and charging control machine.

(51) Step 6: the etching operation was started. All the components in the etchant were automatically charged and balanced by the automatic detection and charging control machine, keeping the concentration of dissociated hydrogen ions, the oxidation-reduction potential and the specific density at the numerical values specified in Table 1.

(52) An etch factor test was carried out using printed circuit boards with size of 620540 mm, copper foil thickness of 1 oz, line width and line spacing of 50.8 m. A pure copper etching rate test board with size of 500300 mm1.5 mm was employed for spray corrosion testing. The etching rate and the etch factor K were calculated using methods known in the art. The calculated results of etching rate and etch factor K are recorded in Table 2.

(53) Testing the Impact of Etchant on Liquid and Dry Film Photoresists:

(54) In comparative example 1 and embodiments 4, 8, 15 and 28, when the various process parameters arrived at set numerical values, printed circuit test boards with the size of 500300 mm1.5 mm, and are coated with either liquid or dry film photoresists, were employed for spray corrosion testing in the etching machine for 1 min. The automatic detection and charging control machine automatically recharged and balanced each component in the etchant, keeping the pH value and the specific density at prescribed numerical values specified in Table 1. The liquid or dry film photoresists were carefully scrutinised and gently scratched using equipment in order to observe whether there is discolouration, softening or stripping of the photoresists.

(55) Data Analysis of Table 1 and 2:

(56) The etching rates of comparative example 2 and embodiments 19 and 21 are similar, all within the range of from 39.1 to 41.2 m/min; they have identical concentration of copper ions (120 g/L). The pH of comparative example 2 is 8.6, and that of embodiments 19 and 21 are 8.2 and 7.7 respectively; the etch factor of comparative example 2 is 3.6, and that of embodiments 19 and 21 are 5.2 and 7.2 respectively.

(57) The etching rate of comparative example 3 (36.0 m/min) is similar to that of embodiment 5 (35.3 m/min); they have identical concentration of copper ions (120 g/L). The pH of comparative example 3 is 8.3, and that of embodiment 5 is 7.2; the etch factor of comparative example 3 is 4.2, whereas that of embodiment 5 is 11.0.

(58) The etching rate of comparative example 4 (28.6 m/min) is similar to that of embodiment 23 (31.0 m/min); both embodiments have identical concentration of copper ions (120 g/L). The pH of comparative example 4 is 8.0, and that of embodiment 23 is 7.7; the etch factor of comparative example 4 is 4.7, whereas that of embodiment 23 is 7.3.

(59) In conclusion, at the same or similar etching rates and concentrations of copper ions, the alkaline cupric chloride etchant of the invention has lower pH value and larger etch factor comparing to alkaline cupric chloride etchants of the prior art.

(60) The pH value and the concentration of copper ions in comparative example 1 are the same as those in embodiment 11, but embodiment 11 has an etching rate which is 1.96 times of that of comparative example 1, and its etch factor is 1.11 times of that of comparative example 1.

(61) Comparative example 2, embodiment 10 and embodiment 18 have the same pH value and concentration of copper ions, whereas the etching rate of embodiment 10 is 1.96 times of that of comparative example 2, and the etch factor K of embodiment 10 is 1.06 times of that of comparative example 2; embodiment 18 has an etching rate which is 1.92 times of that of comparative example 2, and its etch factor is 1.08 times of that of comparative example 2.

(62) The pH value and the concentration of copper ions in comparative example 3 are the same as those in embodiment 9, but embodiment 9 has an etching rate which is 2.06 times of that of comparative example 3, and its etch factor is 1.17 times of that of comparative example 3.

(63) The pH value and the concentration of copper ions in comparative example 4 are the same as those in embodiment 8, but embodiment 8 has an etching rate which is 2.34 times of that of comparative example 4, and its etch factor is 1.28 times of that of comparative example 4.

(64) In summary, at the same pH and concentration of copper ions, the etching rates of etchants of the invention is higher than, and can be as high as more than twice of the etching rate of the prior art.

(65) In addition, at pH<8.0, alkaline cupric chloride etchants in prior art cannot carry out proper etching operation. In contrast, etchants of the present invention maintain relatively high etching rates and good etching quality (e.g. embodiments 4-7, 12-15 and 20-30) at pH<8.0, so they can be used in the etching of PCBs coated with dry-film or liquid photoresists. Currently, acidic cupric chloride etchants are commonly used in the etching of such PCBs, and comparative example 5 is a commonly employed acidic cupric chloride etchant for such purpose. It can be seen in Table 2, when the pH of the alkaline cupric chloride etchants of the invention is low enough to etch PCBs coated with dry-film photoresists (pH<7.8) or liquid photoresists (pH<7.5), the etch factor is significantly larger than that of comparative example 5. Furthermore, a large amount of irritating acidic odour is produced due to evaporation of hydrochloric acid when applying acidic cupric chloride etchants during the etching process. In contrast, the alkaline cupric chloride etchants of the invention with pH 7.0-8.0 have almost no ammonia gas odour at working temperature (about 50 C.).

(66) The results in Table 3 of testing the impact of etchant on liquid and dry film further illustrate that due to the relative high pH of the current alkaline cupric chloride etchants, corrosion of liquid and dry-film photoresists take place. The alkaline cupric chloride etchants of the present invention can be used in etching printed circuit boards coated with dry-film photoresists at pH<7.8, and can be applied to etch printed circuit boards coated with by liquid photoresists when pH<7.5.

(67) TABLE-US-00001 TABLE 1 Parameters of automatic detection and Concen- charging sub-etchant tration control Ammo- Ammo- Ammo- Ammo- Ammo- of machine Formic nium nium nium Citric Malic nium nium copper Specific Etching acid Formate hydroxide chloride water acid acid citrate malate ions density system (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (g/L) pH (g/ml) Comparative 0 0 20 20 58 0 0 0 0 130 8.8 1.19 example Comparative 0 0 20 20 58 0 0 0 0 130 8.8 1.19 example 1 Comparative 0 0 20 20 58 0 0 0 0 120 8.6 1.18 example 2 Comparative 0 0 20 20 58 0 0 0 0 120 8.3 1.18 example 3 Comparative 0 0 20 20 58 0 0 0 0 120 8.0 1.18 example 4 Embodiment 2.55 0 1 20 76.45 0 0 0 0 130 8.2 1.21 1 Embodiment 0 2.55 0 20 77.45 0 0 0 0 130 8.2 1.21 2 Embodiment 1.55 1 0.6 20 76.85 0 0 0 0 130 8.2 1.21 3 Embodiment 2.55 0 1 20 76.45 0 0 0 0 120 7.0 1.20 4 Embodiment 2.55 0 1 20 76.45 0 0 0 0 120 7.2 1.20 5 Embodiment 2.55 0 1 20 76.45 0 0 0 0 120 7.4 1.20 6 Embodiment 2.55 0 1 20 76.45 0 0 0 0 120 7.7 1.20 7 Embodiment 2.55 0 1 20 76.45 0 0 0 0 120 8.0 1.20 8 Embodiment 2.55 0 1 20 76.45 0 0 0 0 120 8.3 1.20 9 Embodiment 2.55 0 1 20 76.45 0 0 0 0 120 8.6 1.21 10 Embodiment 2.55 0 20 20 76.45 0 0 0 0 130 8.8 1.22 11 Embodiment 2.55 0 1 20 76.45 0 0 0 0 30 7.8 1.11 12 Embodiment 2.55 0 1 20 76.45 0 0 0 0 60 7.8 1.14 13 Embodiment 2.55 0 1 20 76.45 0 0 0 0 90 7.8 1.17 14 Embodiment 2.55 0 1 20 76.45 0 0 0 0 90 7.8 1.17 14 Embodiment 2.55 0 1 20 76.45 0 0 0 0 114 7.8 1.19 15 Embodiment 2.55 0 1 20 76.45 0 0 0 0 140 8.2 1.22 16 Embodiment 2.55 0 1 20 76.45 0 0 0 0 170 8.2 1.25 17 Embodiment 0.0002 0 25 30.0 44.9998 0 0 0 0 120 8.6 1.20 18 Embodiment 0.81 0 0.5 23.0 75.69 0 0 0 0 120 8.2 1.20 19 Embodiment 4.2 0 2 23.0 70.8 0 0 0 0 120 7.7 1.20 20 Embodiment 8.5 0 10 23.0 58.5 0 0 0 0 120 7.7 1.20 21 Embodiment 12.7 0 7 23.0 57.3 0 0 0 0 120 7.7 1.20 22 Embodiment 17.0 0 9 23.0 51 0 0 0 0 120 7.7 1.20 23 Embodiment 25 0 13 10 52 0 0 0 0 60 7.7 1.21 24 Embodiment 2.55 0 1 25 71.45 0 0 0 0 80 7.7 1.16 25 Embodiment 2.55 0 1 15 81.45 0 0 0 0 80 7.7 1.16 26 Embodiment 2.55 0 1 10 86.45 0 0 0 0 80 7.7 1.16 27 Embodiment 0 0 1 20 76.45 1 0 0 0 120 7.5 1.20 28 Embodiment 0 0 1 20 76.45 0 1.5 0 0 120 7.4 1.20 29 Embodiment 1 0 0.3 20 76.45 0 0 0.7 0.8 120 7.4 1.20 30

(68) TABLE-US-00002 TABLE 2 Etching Etch Environmental Etching system rate (m/min) factor K impact Comparative 40.2 2.8 Obvious example 1 ammonia smell Comparative 40.0 3.6 Obvious example 2 ammonia smell Comparative 36.0 4.2 Slight ammonia example 3 smell Comparative 28.6 4.7 Slight ammonia example 4 smell Comparative 35 1.7 Obvious acidic example 5 odour Embodiment 1 49.5 5.3 Slight ammonia smell Embodiment 2 49.5 5.4 Slight ammonia smell Embodiment 3 49.5 5.4 Slight ammonia smell Embodiment 4 24.4 13.6 Almost no ammonia smell Embodiment 5 35.3 11.0 Almost no ammonia smell Embodiment 6 53.0 8.5 Almost no ammonia smell Embodiment 7 62.5 7.3 Almost no ammonia smell Embodiment 8 67.0 6.0 Slight ammonia smell Embodiment 9 74.1 4.9 Slight ammonia smell Embodiment 10 78.3 3.8 Slight ammonia smell Embodiment 11 78.6 3.1 Obvious ammonia smell Embodiment 12 18.2 6.9 Almost no ammonia smell Embodiment 13 39.1 6.9 Almost no ammonia smell Embodiment 14 64.6 6.8 Almost no ammonia smell Embodiment 15 61.1 7.0 Almost no ammonia smell Embodiment 16 76.0 5.3 Slight ammonia smell Embodiment 17 32.9 5.1 Slight ammonia smell Embodiment 18 76.9 3.9 Obvious ammonia smell Embodiment 19 41.2 5.2 Slight ammonia smell Embodiment 20 50.9 7.3 Almost no ammonia smell Embodiment 21 39.1 7.2 Almost no ammonia smell Embodiment 22 48.5 7.4 Almost no ammonia smell Embodiment 23 31.0 7.3 Almost no ammonia smell Embodiment 24 14.2 7.5 Almost no ammonia smell Embodiment 25 71.2 7.4 Almost no ammonia smell Embodiment 26 26.5 7.2 Almost no ammonia smell Embodiment 27 20.6 7.2 Almost no ammonia smell Embodiment 28 50.5 8.4 Almost no ammonia smell Embodiment 29 48.3 8.5 Almost no ammonia smell Embodiment 30 49.7 8.4 Almost no ammonia smell

(69) TABLE-US-00003 TABLE 3 Type of Observation of etch Etching system pH value photoresist resist Comparative 8.8 dry-film No discolouration; partly example 1 striped after gentle scratching liquid No discolouration; partly striped after gentle scratching Embodiment 4 7.0 dry-film Not discoloured, softened or striped liquid Not discoloured, softened or striped Embodiment 28 7.5 dry-film Not discoloured, softened or striped liquid Not discoloured, softened or striped Embodiment 15 7.8 dry-film Not discoloured, softened or striped liquid No discolouration; partly striped after gentle scratching Embodiment 8 8.0 dry-film No discolouration; partly striped after gentle scratching liquid No discolouration; partly striped after gentle scratching