Lead frame and method for manufacturing the same

Abstract

A metal plate 1 to be a lead frame has a plating with Sn or Zn or a plating with various alloys containing these metals only on the side faces and half-etched faces 6, and a noble metal plating layer formed on the front surface as a surface on which a semiconductor device is to be mounted.

Claims

1. A lead frame made of a metal plate, wherein a plating of Sn, Zn or various alloys containing these metals, including ZnNi, SnBi, SnCu and SnB, is formed only on side faces and half-etched faces of the lead frame.

2. The lead frame according to claim 1, wherein a thickness of the plating of any of the various alloys is 0.02 to 2.0 μm.

3. The lead frame according to claim 1, wherein a noble metal plating layer is formed on a lead frame surface on which a semiconductor element or an LED element is to be mounted.

4. The lead frame according to claim 3, wherein the noble metal plating layer is formed of Ni (or Ni alloy)/Pd (or Pd alloy), Ni (or Ni alloy)/Pd (or Pd alloy)/Au (or Au alloy), Ni (or Ni alloy)/Pd (or Pd alloy)/Au (or Au alloy)/Ag (or Ag alloy), Ni (or Ni alloy)/Pd (or Pd alloy)/Ag (or Ag alloy)/Au (or Au alloy), Cu (or Cu alloy)/Ag (or Ag alloy) overlaid one after another in this order.

5. The lead frame according to claim 3, wherein, other than the lead frame surface on which the noble metal layer is formed, faces of the metal plate are left uncovered.

6. A method for manufacturing a lead frame comprising: a step of forming a plating mask of a resist on a metal plate that is a material of the lead frame; a step of plating the metal plate left uncovered with the plating mask; a step of forming an etching mask of a resist, to cover the plated portion for attaining a required shape of the lead frame; a step of subjecting the metal plate to through-hole work and a half-etching work by etching; and a step of plating through-hole faces and half-etched faces worked by etching with Sn, Zn or various alloys containing these metals.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1A-I are views that show steps of the method for manufacturing a lead frame according to a first embodiment of the present invention, in which FIG. 1A is a view in which a resist layer is formed on a metal plate, FIG. 1B is a view in which a plating mask is formed, FIG. 1C is a view in which a plating layer is formed, FIG. 1D is a view in which the plating mask is peeled off, FIG. 1E is a view in which a resist layer is formed on both surfaces of the metal plate which has been plated, FIG. 1F is a view in which an etching mask is formed, FIG. 1G is a view after etching, FIG. 1H is a view in which plating treatment with Sn, Zn or various alloys containing these metals is locally carried out using the etching mask, and FIG. 1I is a view in which the etching mask is peeled off.

(2) FIG. 2 is a table that shows evaluation results of resin adhesion strength of test pieces prepared in Embodiments and Comparative Examples.

MODE FOR CARRYING OUT THE INVENTION

(3) Hereinafter, a method for manufacturing a lead frame according to the present invention will be described with reference to FIGS. 1A-I.

(4) A first step is the step of: forming a photoresist layer 2 by laminating a photoresist on the front and back surfaces of a metal plate 1 to be a lead frame material, putting on the photoresist layer 2 a plating mask 3 that carries a plating pattern, and drawing the plating pattern by transferring it to the resist through a photolithography process (exposure and development).

(5) This step includes: laminating a photoresist (for example, a dry film resist) on the metal plate 1 (FIG. 1A), transferring a glass mask that carries a plating pattern to the resist through a photolithography process (exposure and development), to draw the plating pattern on the metal plate 1 (FIG. 1B), and then applying Ni/Pd/Au or Ag plating 4 by electrolytic plating, to form Ni/Pd/Au or Ag coating (FIG. 1C).

(6) Next is: peeling off the plating mask 3 formed on the both surfaces of the metal plate 1 with an aqueous solution of sodium hydroxide (FIG. 1D), and then laminating a photoresist again on the metal plate 1 (FIG. 1E), transferring a glass mask that carries a lead frame pattern to the resist through a photolithography process (exposure and development) (FIG. 1F), and removing unnecessary metal portions by etching using a ferric chloride solution, to form a lead frame shape (FIG. 1G).

(7) Next is performing Sn or Zn plating treatment by electrolytic plating (FIG. 1H). As a result, Sn or Zn plating is applied with a thickness of 0.02 to 2.0 μm only to the etching-dissolved faces (side faces and half-etched portions of the metal plate 1).

(8) Finally, peeling off the etching mask formed on the both surfaces of the metal plate 1 with an aqueous solution of sodium hydroxide makes the lead frame (FIG. 1I) according to the present invention.

(9) In this way, the present invention can provide a lead frame with an improved adhesion to the sealing resin and a wire bondability equivalent to that of the conventional one. According to the present invention, a copper-based material is preferable as the material of the metal plate 1, but it is not limited thereto.

Embodiment 1

(10) Using a copper material having a thickness of 0.150 mm as the metal plate 1, a dry film resist (Asahi Kasei E-Materials Co., Ltd.: AQ-2058) was affixed to the both surfaces to form a resist layer. Then, by performing exposure and development using a glass mask for the upper surface side and the rear surface side on which a pattern for forming the plating is formed, the resist in the portions for plating is removed, to thereby form a plating mask that leaves the metal plate surface partially uncovered.

(11) Next, a plating process was performed to form a plating on the uncovered portions of the metal plate surface. In this embodiment, Ni plating with a set value of 1.0 μm, Pd plating with a set value of 0.02 μm, and Au plating with a set value of 0.007 μm were applied in order from the metal plate side, to form a three-layered plating.

(12) Next, the plating masks formed on both sides of the metal plate were peeled off with a 3% sodium hydroxide aqueous solution, and washing treatment with a 3% sulfuric acid was also carried out.

(13) Next, a dry film resist (Asahi Kasei E-Materials Co., Ltd.: AQ-44096) was affixed to the both sides of the plated metal plate to form a resist layer, and a glass mask carrying a lead frame shape was used. And both surfaces were exposed and developed to form an etching mask.

(14) Next, a spray etching process was performed using a ferric chloride solution to form a lead frame. In the etching process, a ferric chloride solution having a liquid temperature of 70° C. and a specific gravity of 1.47 was used, to be sprayed at a set pressure of 0.3 MPa by a swinging spray nozzle for about 160 seconds of the treatment.

(15) Next, after removal of copper crystals, which had adhered to the etching-dissolved faces, by washing with sulfuric acid via spraying, Zn plating treatment was performed by electrolytic plating method. This electric Zn plating bath contained 5 g/l of NaOH, 35 g/l of NaCN and 230 g/l of Zn(CN), and electric Zn plating was carried out at a current density of 3 Å/dm.sup.2, to obtain a Zn plating layer with a film thickness of 1 μm.

(16) Next, the residue of the Zn plating treatment liquid, which had adhered to the Zn plating surface, was removed by washing with hydrochloric acid via spraying, and then the etching mask was peeled off using an aqueous solution of sodium hydroxide. Thereafter, acid treatment with sulfuric acid was carried out to dry the surface, thereby obtaining a lead frame of Embodiment 1 in which the product side surface and the etching-dissolved faces were locally Zn-plated.

Embodiment 2

(17) A lead frame of Embodiment 2 was obtained in the same manner as in Embodiment 2 except that the film thickness of the electric Zn plating was 0.2 μm.

Embodiment 3

(18) A lead frame of Embodiment 3 was obtained in the same manner as in Embodiment 1 except that Sn plating was applied instead of Zn. This electric Sn plating bath contained 55 g/l of stannous sulfate, 100 g/l of sulfuric acid, 60 g/l of cresolsulfonic acid, 2 g/l of gelatin, and 1 g/l of β-naphthol, and an electric Sn plating was carried out at a current density of 2 A/dm.sup.2, to obtain a Sn plating layer with a film thickness of 1 μm.

Embodiment 4

(19) A lead frame of Embodiment 4 was obtained in the same manner as in Embodiment 1 except that ZINNY ST AF 210 zinc nickel alloy plating (Ni codeposition rate 12-15 wt %) manufactured by Atotech Co., Ltd., was applied to the Zn plating. ZINNY ST AF 210 zinc nickel alloy plating was a plating bath composed of a basic solution that contained 213 g/l of potassium chloride, 42 g/l of zinc chloride and 121 g/l of nickel chloride hexahydrate and, as additives, 10 ml/l of ZINNY ACAF 211, 10 ml/l of ZINNY ACAF 212, 20 ml/l of ZINNY ACAF 214, and 70 ml/l of ZINNY ACAF 216, and electric plating was carried out at a current density of 2 A/dm.sup.2, to obtain a ZnNi alloy plating layer with a film thickness of 1 μm.

Embodiment 5

(20) A lead frame of Embodiment 5 was obtained in the same manner as in Embodiment 1 except that NiP plating was applied instead of Ni. This electric NiP plating bath was contains 250 g/l of nickel sulfate, 50 g/l of nickel chloride, 50 g/l of boric acid and 30 ml/l of Novoplate HS (Atotech Japan Kabushiki Kaisha) and electric Sn plating was carried out at a current density of 2 A/dm.sup.2, to obtain a NiP plating layer with a film thickness of 1 μm.

(21) Although the embodiments have been described above, the present invention is not limited by these embodiments.

Comparative Example 1

(22) A lead frame of Comparative Example 1 was obtained in the same manner as in Embodiment 1 except that Zn plating was not applied after etching.

Comparative Example 2

(23) A lead frame of Comparative Example 2 was obtained in the same manner as in Embodiment 1 except that copper roughening treatment was performed instead of Zn plating after etching. The copper roughening treatment was carried out by spraying a roughening treatment liquid (Mech Co., Ltd.: CZ 8100). Upon this roughening treatment liquid being conditioned to a liquid temperature of 35° C., a specific gravity of 1.145, and a copper concentration of 35 g/L, roughening treatment was performed by spraying. The surface roughness of the roughened surface was SRa 0.2-0.4.

Comparative Example 3

(24) A lead frame of Comparative Example 3 was obtained in the same manner as in Embodiment 1 except that Ag plating was applied instead of Zn plating. The Ag plating bath contains 40 g/l of KCN, 35 g/l of AgCN and 22 g/l of K.sub.2CO.sub.3, and Ag electroplating was carried out at a current density of 3 A/dm.sup.2, to obtain an Ag plating layer with a film thickness of 0.2 μm.

(25) test pieces for the resin adhesion evaluation test was cut out from the lead frames thus formed.

(26) In order to judge the resin adhesion of these test pieces, the resin adhesion strength was evaluated by the following method. That is, on a metal base material, four pieces of the resin having a diameter of 2 mm were formed under the conditions of a metal injection pressure of 100 kg/cm.sup.2 and a metal mold temperature of 175° C. for 90 seconds, and the pieces of resin were heated in an oven at 175° C. for 8 hours And subjected to curing treatment to form four samples for evaluation. Each of the resin samples for evaluation was pushed right from the side, and the load at the time when the resin peeled off was measured. This value was divided by the adhesion area of the resin and converted into the load per unit area. The average of the loads of the four samples thus obtained was taken as the resin adhesion strength.

(27) As a result of evaluation of resin adhesion strength for each of the lead frames produced according to Embodiments and Comparative Examples as described above, as shown in FIG. 2, the resin adhesion strength was 23 MPa regarding the lead frame of Embodiment 1, 23 MPa also regarding the lead frame of Embodiment 2, 19 Mpa regarding the lead frame of Embodiment 3, 19 Mpa regarding the lead frame of Embodiment 4, 19 Mpa regarding the lead frame of Embodiment 5, 10 Mpa regarding the lead frame of Comparative Example 1, 13 MPa regarding the lead frame of Comparative Example 2, and 12 MPa regarding the lead frame of Comparative Example 3.

(28) From these results, it was confirmed that if Sn or Zn plating was applied only to the product-side surface and the half-etched faces, adhesion strength about twice that in the case where Sn or Zn plating was not applied was achieved. Further, when the plating thickness of Zn was in the range of 0.2 to 1 μm, the adhesion strength did not change and was at a sufficiently high level. In addition, it was found that high adhesion strength like Sn or Zn plating cannot be obtained when copper roughening treatment or Ag plating was performed instead of Sn or Zn plating.

(29) On the other hand, even when ZnNi plating or NiP plating was performed, it was found that high adhesion strength as high as that of Sn or Zn plating can be achieved.

DESCRIPTION OF THE REFERENCE SYMBOLS

(30) 1 . . . metal plate 2 . . . resist layer 3 . . . plating mask 4 . . . plating 5 . . . etching mask 6 . . . surface treated with Sn or Zn plating