Process for electroless copper deposition on laser-direct structured substrates

Abstract

The invention disclosed relates to an aqueous activator solution and a method for the electroless deposition of copper on a laser direct structured substrate surface. By the invention, an aqueous activator solution comprising a strong reducing agent is proposed to enhance the catalytic activity of the irradiated surface area of a LDS substrate.

Claims

1. A process for activating seeds in a laser direct structured substrate followed by electroless deposition of a copper layer on a surface of the laser direct structured substrate, the process comprising the steps of: contacting the laser direct structured substrate with an activator solution comprising a reducing agent having a Nernst reduction potential E+0.35V to activate exposed metal seeds in the laser direct structured substrate; and contacting the activated substrate with an electroless copper plating composition.

2. The process according to claim 1 wherein the substrate is contacted with the activator solution at a temperature in a range of between 5 C. and 95 C.

3. The process according to claim 1 wherein the substrate is contacted with the activator solution for a time in a range of between 10 s and 30 min.

4. The process according to claim 1 wherein the substrate at least partially is made from a material of the group consisting of polyamides (PA), poly urethane resins (PU), acrylonitrile butadiene styrene (ABS), poly carbonate (PC), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), liquid crystal polymers (LCP), polyphthalamide (PPA), a blend, a co-polymerisate, or a composite-structure of these.

5. The process according to claim 1 wherein the reducing agent is at least one compound of the group consisting of an alkali borohydride, an alkali sulphite, an alkali dithionite, an alkali thiosulfate, and zinc, or a mixture of these.

6. The process according to claim 1 wherein the reducing agent is at least one compound of the group consisting of sodium borohydride, lithium borohydride, dimethylaminoborane, sodium sulphite, lithium sulphite, sodium dithionite, lithium dithionite, sodium thiosulfate, sodium hypophosphite, and lithium thiosulfate, formaldehyde, ammonium form iate, glyoxalic acid, resorcin, hydrazine, hydrazine hydrate, or a mixture of these.

7. The process according to claim 1 wherein the reducing agent is in the activator solution in a range of between 0.001 mol/l and 5.0 mol/l.

8. The process according to claim 1 wherein the activator solution additionally comprises at least one additive of the group consisting of stabilizers, complexing agents, and surfactants.

9. The process according to claim 1 wherein the activator solution has a pH value in a range of between 0 and 14.

10. The process according to claim 1, the process further comprising, prior to the contacting the laser direct structured substrate with the activator solution: laser structuring a substrate comprising non-conductive metal-organic compounds embedded in a non-conductive substrate to release metal seeds to produce the laser direct structured substrate; wherein contacting the laser direct structured substrate with the activator solution activates the metal seeds for subsequent electroless deposition of copper.

11. The process of claim 8 wherein the contacting with the electroless copper plating composition is performed with no copper plating operation between the contacting with the activator solution and the contacting with the electroless plating composition.

12. The process of claim 1 wherein the copper plating is performed with a single plating step.

13. A process for the electroless deposition of a copper layer on a surface of a laser direct structured substrate, the process comprising the steps of: contacting a laser direct structured substrate with an activator solution comprising a reducing agent having a Nernst reduction potential E+0.35V to activate exposed metal seeds in the laser direct structured substrate; thereafter contacting the substrate with a metal salt solution, wherein the metal salt solution is different from the activator solution; and thereafter contacting the activated substrate with an electroless copper plating composition.

14. The process according to claim 13 wherein the metal salt solution comprises at least one of CuSO.sub.4 and PdCl.sub.2.

15. The process according to claim 13 wherein the concentration of the metal salt in the metal salt solution is in the range of between 0.0001 mol/l to 0.1 mol/l.

16. The process of claim 13 wherein the contacting with the electroless copper plating composition is performed with no copper plating operation between the contacting with the activator solution and the contacting with the electroless plating composition.

17. The process of claim 13 wherein the copper plating is performed with a single plating step.

Description

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(1) With respect to the means for improving the process of copper deposition, by the invention an aqueous activator solution for laser direct structured substrates is proposed, said solution comprising a strong reducing agent.

(2) Surprisingly is was found that when contacting a laser direct structured substrate prior to an electroless plating with an activator solution comprising a strong reducing agent a significant improved copper deposition is achieved. It is believed that the reducing agent enhances the catalytic activity of the irradiated surface of the LDS substrate and due to that, which in turn improves the initiation of the electroless copper deposition. In consequence, the time for initiating and plating are significantly reduced. Furthermore, the electroless copper electrolyte can be operated thermodynamically and kinetically on a lower level of energy by which the stability of the deposition process as well as of the electrolyte used is increased. This gives significant environmental and economical befit to the process in comparison the electroless processes known from the state of the art.

(3) Additionally, due to the improved deposition the use of a second copper process to build up the desired thickness of the deposited copper layer is obsolete. This results in a reduction of the overall process time for the copper plating step, which in turn gives further economic benefit to the invention.

(4) According to an embodiment of the invention, the activator solution comprises a reducing agent having a Nernst reduction potential E+0.35 V.

(5) The Nernst reduction potential is calculated according to the following formula:

(6) $E=E^o+\frac{\mathrm{RT}}{z_{e}F}\ln \frac{a_{\mathrm{Ox}}}{a_{\mathrm{Red}}}$

(7) wherein E is the reduction potential, E is the standard reduction potential, R is the universal gas constant, T is the absolute temperature in K, a is the chemical activity of the relevant redox partner which can be substituted by the simple concentration of the redox partner, F is the Faraday constant, and z.sub.e is the number of electrons transferred in the redox reaction.

(8) It was found that a reducing agent having such a reduction potential is capable to enhance the catalytic activity of the irradiated surface of the LDS substrate.

(9) According to another embodiment of the invention, the reducing agent comprised in the activator solution is at least on one compound of the group consisting of an alkali borohydride, an alkali sulphite, an alkali dithionite, an alkali thiosulfate, and zinc, or a mixture of these. Preferably, the reducing agent comprised in the activator solution is at least one compound of the group consisting of sodium borohydride, lithium borohydride, dimethylaminoborane, sodium sulphite, lithium sulphite, sodium dithionite, lithium dithionite, sodium thiosulfate, sodium hypophosphite, and lithium thiosulfate, formaldehyde, ammonium formiate, glyoxalic acid, resorcin, hydrazine, hydrazine hydrate, or a mixture of these.

(10) According to another embodiment of the invention, the reducing agent can be comprised in the activator solution in a range of between 0.001 mol/l and 5.0 mol/l. It was found that already at a concentration of more than 0.001 mol/l a significant enhancement of the catalytic activity of the irradiated surface of the LDS substrate is achieved.

(11) In another embodiment of the invention, the activator solution additionally comprises at least one additive of the group consisting of stabilizers, complexing agents, and surfactants. Examples for such additives are phenantrolines, like 1,10-phenantrolinium chloride, bipyridine, phenanthrenes, like neocuproin, chinolines, like benzochinoline and cuproin-2,2-bichinoline, bathocuproinedisulfonic acid, dithizone, diphenylcarbazone, diphenylcarbazide, azo compounds, like methyl orange, five membered heterocyclic rings, like pyrrole, pyrazole, imidazole, 1,2,4-triazole, 1,2,4-benzotriazole, thiophene, and thiazole, six membered heterocyclic rings, like pyridine, and nicotinic acid, thiourea, urea, dithiooxamide, 2-mercaptobenzothiazole, acetamide, sodium cyanide, reinecke salt (NH.sub.4[Cr(NCS).sub.4(NH.sub.3).sub.2].Math.H.sub.2O), cuprone (-benzoin oxime) [alpha-benzoin oxime], and cupferrone (ammonium salt of N-nitroso-N-phenylhydroxylamine).

(12) In another preferred embodiment of the invention, the activator has a pH value in a range of between pH 0 and pH 14. Surprisingly, it was found that the inventive activator solution can work over the hole spectra of pH value, from strong acidic to strong alkaline, depending on the reduction agent comprised.

(13) In another aspect the invention relates to a process for the electroless deposition of a copper layer on a surface of a laser direct structured substrate, the process comprising the steps of: providing a laser direct structured substrate; contacting the provided substrate with an aqueous activator solution for laser direct structured substrates, said solution comprising a strong reducing agent to achieve an activated substrate; and contacting the activated substrate with an electroless copper plating electrolyte.

(14) Preferably, the LDS substrate is contacted with the activator solution at a temperature in a range of between 5 C. and 95 C., with a preferred range of between 15 C. and 40 C.

(15) It is further preferred, that the LDS substrate is brought into contact with the activator solution for a time in a range of between 10 seconds and 60 minutes. To be brought into contact should be understood as, e.g. dipping the substrate into an activator solution, spraying an activator solution onto the substrate or any other appropriate way to enable a chemical reaction of the reducing agent comprised in the activator solution with the irradiated surface area of the LDS substrate.

(16) Surprisingly it was found, that the inventive process is capable to improve the electroless copper deposition on any commonly LDS substrate material, like e.g. polyamides (PA), poly urethane resins (PU), acrylonitrile butadiene styrene (ABS), poly carbonate (PC), polyethylene terephthalte (PET), polybutylene terephthalate (PBT), liquid crystal polymers (LCP), polyphthalamide (PPA), a blend, a co-polymerisate, or a composite-structure of these. Examples for commercially available materials are Ultramid T 4381 LDS, Ultramid T 4381 LDS sw 23215, Ultradur B4300GM24 LDS, (all available from BASF AG); Pocan DP7102 LDS, Pocan DPT7140 LDS (both available from Lanxess); Vectra E840i LDS (available from Ticona GmbH); RTP 2599 X 113384 A, RTP 2599 X 113384 C, RTP 2599 X 113384 D, RTP 399 X 113385 B, RTP 3499-3 X 113393 A, RTP 4099 X 117359 D (all available from RTP Co.); StanylForTii NC 1107A, StanylForTii NC 1119D (available from DSM Engeneering Plastics B.V.); Xantar LDS 3710, Xantar RC 3711, Xantar LDS 3720, Xantar RC 3722, Xantar RC 3723, Xantar LDS 3730, Xantar RX 3732, Xantar RX 3733, lupilon MTB1000R 8920F (all available from Mitsubishi Engineering-Plastics Corporation); Vestodur X9423, Vestamid HTplus TGP 3586, Vestamid HTplus TGP 3586 (available from Evonik Industries); TPJF231 F (available from Wah Hong Industrial Corp.); NX07354, NX07354P, NX10302, UX08325, NX11302 (all available from Sabic Innovative Plastics); and Grilamid 1SBVX-50H LDS (available from EMS-Chemie AG).

(17) The invention is described further in terms of the following examples.

(18) A LDS (Laser Direct Structured) substrate is treated by according to the following process steps (Rinsing between the steps is optional and not listed separately):

(19) 1) Cleaning of the substrate in an acid or alkaline cleaner solution, depending of the stability of the plastic, at a temperature from ambient up to 50 C., for 5 min up to 20 min;

(20) 2) Dipping of the cleaned substrate in an inventive activator solution comprising a reducing agent at a temperature from 25 C. up to 90 C., from 5 min up to 1 h;

(21) 3) Optional: Dipping of the activated substrate in a metal salt containing solution, at a temperature from ambient to about 50 C. for 5 min up to 30 min;

(22) 4) Dipping the pretreated substrate in an electroless copper plating solution like LDS Cu 400 (available from Enthone Corp.) at a temperature from 30 C. up to 70 C. 30 min up to 2 hours, depend of the thickness of the deposition to be achieved.

(23) The metal salt containing solution used in the optional step 3) contains a metal salt like CuSO.sub.4, PdCl.sub.2, or salt of another suitable metal in the concentration of 0.0001 mol/l to 0.1 mol/l.

(24) If the activator solution used in step 2) is an alkaline solution, a subsequent acid rinse step or an acid post dip step is recommended.

(25) The following table comprises examples of activator solution compositions according to the invention. Acidic environment means about pH 2 or below, neutral environment means about pH 5 to 8, and alkaline environment means about pH 12 or above. The concentration of the reducing agent within the activator solution was 0.01 mol/l.

(26) TABLE-US-00001 Result (improvement in plating result) Pretreatment (reduction agent signif- indif- in activator solution) T/ C. major icant ferent NaH.sub.2PO.sub.2H.sub.2O pH conditions Acidic 50 X neutral 50 X HCHO pH environment neutral 50 X alkaline 50 X NaH.sub.2PO.sub.2/DMAB pH environment acidic 35 X neutral 35 X alkaline 35 X acidic 50 X neutral 50 X alkaline 50 X acidic 70 X neutral 70 X alkaline 70 X NaBH.sub.4 pH environment alkaline 35 X alkaline + NaCl 35 X Ascorbic acid, C.sub.6H.sub.8O.sub.6 pH environment acidic 35 X neutral 35 X alkaline 35 X acidic 50 X neutral 50 X alkaline 50 X acidic 70 X neutral 70 X alkaline 70 X Experiments with metal containing solutions as post dip treatment (reducing agent in activator solution, conditions in activator solution, metal salt in post dip, conditions in post dip) CuSO.sub.4 pH environment CuSO.sub.4, acidic 35 X HCHO, alkaline + CuSO.sub.4, acidic 50/35 X DMAB, alkaline + CuSO.sub.4, acidic 50/35 X NaBH.sub.4/NaCl, alkaline + CuSO.sub.4, 35/35 X acidic NaBH.sub.4, alkaline + CuSO.sub.4, acidic 35/35 X PdCl.sub.2 pH environment PdCl.sub.2, acidic 35 X DMAB, alkaline + PdCl.sub.2, acidic 35/35 X NaBH.sub.4/NaCl, alkaline + PdCl.sub.2, 35/35 X acidic NaBH4/NaCl, alkaline + PdCl2, 50/50 X acidic

(27) When introducing elements of the present invention or the preferred embodiment(s) thereof, the articles a, an, the and said are intended to mean that there are one or more of the elements. The terms comprising, including and having are intended to be inclusive and mean that there may be additional elements other than the listed elements.

(28) As various changes could be made in the above without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense. The scope of invention is defined by the appended claims and modifications to the embodiments above may be made that do not depart from the scope of the invention.