JPH0766342A - Lead frame manufacturing method - Google Patents

Abstract

(57) [Summary] [Purpose] In the method of manufacturing a copper-based lead frame, various elements added to the copper-based alloy include casein, PVA.
By suppressing the reaction at the interface of the lead frame with the dichromate ion of the photosensitizer added to the photosensitizer such as, and improving the resolution accuracy of the resist pattern,
The challenge is to provide a lead frame with an extremely large number of pins so that it can handle finer patterns. [Constitution] Casein containing a dichromate-based photosensitizer in an etching resist of a lead frame material made of a copper alloy, P
A method of forming a desired resist pattern using a photosensitive solution such as VA and then etching, by forming a copper plating layer on the surface of a copper alloy before the photosensitive solution coating step, the dimensional accuracy is improved, This is a method for manufacturing a lead frame that reduces variations.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a lead frame used for manufacturing semiconductor electronic parts and the like.

[0002]

2. Description of the Related Art Generally, 42 alloys and copper alloys are used as lead frame materials for semiconductor devices, but recently, due to improvement in device density, various copper alloys with excellent heat conduction and conductivity have been used. The usage rate is increasing. The lead frame is composed of a die pad part on which a silicone chip is mounted, an inner lead part to which a wire is connected, and an outer lead part for input / output with the outside. The silicone chip is attached to the die pad portion of the lead frame by Au-Si eutectic bonding, bonding with a conductive paste agent, or soldering. The electrode pad on the chip and the tip of the inner lead portion are connected by Au wire, Al wire, or Cu wire by thermocompression bonding or ultrasonic thermocompression bonding. At this time, the lead frame material is required to have a predetermined strength at the time of handling and processing, and the characteristics are satisfied by adding various elements and alloying.

A press method and an etching method are used in the manufacture of the copper-based lead frame, but the etching method is the mainstream for a lead frame having a large number of pins. In the etching method, a photosensitive solution such as casein or PVA containing a dichromic acid-based photosensitizer is applied to the surface of the lead frame material, and after drying, a desired pattern is exposed and developed to form an etching pattern. A metal pattern is formed by dissolving an unnecessary portion of this using an etching solution of ferric chloride or cupric chloride. However, various elements are added to the copper alloy, and the dichromate ion of the photosensitizer added to the photosensitizer and the additive element in the copper alloy are metal elements that are less base than copper in terms of redox potential. However, there is a problem in that a local battery is formed at the interface of the lead frame material and it reacts electrochemically to deteriorate the pattern resolution accuracy.

[0004]

DISCLOSURE OF THE INVENTION The present invention is directed to a method for manufacturing a copper-based lead frame, wherein among the various elements added to the copper alloy, the metal element that is less base than copper in terms of redox potential is casein. Resist patterns that form a local battery at the interface between the dichromate ion of the photosensitizer added to the photosensitizer such as PVA and the lead frame material and electrochemically reduce the dichromate ion. It is an object to supply a lead frame with an ultra-high pin count by making it possible to deal with finer patterns by improving the resolution accuracy of.

[0005]

According to a first aspect of the present invention, there is provided a casein containing a dichromate-based photosensitizer in an etching resist of a lead frame material made of a copper alloy,
A lead frame characterized by forming a desired resist pattern using an aqueous photosensitive solution such as PVA and then etching, wherein a copper plating layer is formed on the surface of a copper alloy before the photosensitive solution applying step. Is a manufacturing method. According to a second aspect of the present invention, in the method according to the first aspect, the thickness of the copper plating layer is set to 3 μm or more.

In the present invention, as the copper alloy used as the lead frame material, Cu--Fe--P type alloy, C
u-Ni-Si based alloy, Cu-Sn-P based alloy, Cu-
Conventionally used copper alloys such as Ni-Zn alloys and Cu-Ni-Sn alloys can be used. The method of forming a copper plating film on this copper alloy can be performed by plating using a conventional copper sulfate plating bath, a copper bromide plating bath, a pyrophosphoric acid plating bath, or the like. For plating pretreatment, use chemicals and processes suitable for each plating bath, such as degreasing of the copper surface, pickling, and soft etching.

As the binder of the photosensitive liquid, casein,
PVA, gelatin, etc. can be used. Photosensitivity can be imparted to these binders by adding dichromate ions such as ammonium dichromate and potassium dichromate as a photosensitizer. The method of applying the photosensitive liquid to the lead frame material can be performed by using a dipping method, a spin coating method, or the like. The resist film can be dried by using a hot air drying method, an infrared drying method or the like. Ultraviolet rays (UV) are used for exposing the resist, and any light source capable of irradiating with ultraviolet rays such as a high pressure mercury lamp or an ultrahigh pressure mercury lamp may be used. Hot water is used for developing the resist, and pure water, hard water, soft water or the like can be used as water. The resist film formed by development is cured by using an acid such as chromic acid and heat-treated to obtain a resist film resistant to etching.

[0008]

In the present invention, by forming an electrolytic copper-plated film on the surface of the copper-based lead frame material, among the various elements added to the copper alloy, the redox potential is lower than that of copper. Stable metal elements form a local battery at the metal interface with dichromate ions in the water-based resist and suppress electrochemical reaction, and the shape of the resist pattern is affected by factors other than exposure. Is to suppress. When electrolytic copper plating is performed on the surface of a copper alloy and then an etching pattern is formed with a water-based resist containing dichromate ions, the pattern dimension is close to the mask pattern dimension, and it is confirmed that the dimension variation is reduced. .

[0009]

EXAMPLES The present invention will be described below with reference to examples. (Example) As a copper material, the following No. 1 and No. 2 of 2
Seed material was used. No. 1 is Cu-3.2 wt% N
i-0.7 wt% Si-0.3 wt% Zn, No. Two
Is Cu-2.0 wt% Sn-0.2 wt% Ni-0.
It is 04 wt% P-0.15 wt% Zn, and the plate thickness is 0.15 mm in each case. This material was washed with an alkaline degreasing solution, then pickled, and then subjected to copper plating and post-treatment in a copper sulfate plating bath under the following conditions. Copper sulfate plating conditions Copper sulfate pentahydrate 230 g / l Liquid temperature 25 ° C. Sulfuric acid 60 g / l Anode electrolytic copper hydrochloric acid 50 mg / l Current density 5 A / dm ² Spin a casein photosensitive solution containing ammonium dichromate on this surface It was applied with a coater and dried with a hot air dryer. A negative mask was brought into close contact with this resist surface, vacuum suction was performed with a vacuum exposure machine, and then UV exposure was performed. This resist was developed with a spray developing machine of warm pure water, hardened with a chromic anhydride aqueous solution, and then dried with hot air to form an etching pattern. This was etched with a ferric chloride-hydrochloric acid type etching solution, and the resist was stripped with an alkaline solution of sodium hydroxide.

(Comparative Example) As a copper material, N of the above-mentioned embodiment was used.
o. 1 and No. Two materials of No. 2 were used. After alkaline degreasing, the copper plating step was not performed, and the casein photosensitive solution containing ammonium dichromate was applied to the surface of the lead frame material in the same manner as in the example, and the same procedure as in the above example was performed. A sample was created in the process of.

Next, with respect to the negative pattern 100 μm portion, the resist pattern formed by the process of the example and the resist pattern formed by the process of the comparative example (without copper plating) are compared with the copper plating thickness. The changes in dimensions and variations are shown in Table 1 and FIG.

[Table 1] The resist pattern dimension change in Table 1 is shown in FIG.
The change in the dimensional variation 3σ of is shown in FIG. As shown in Table 1 and FIGS. 1 (a) and 1 (b), the copper plating according to the present invention does not sufficiently cover the surface of the copper material and the resist interfacial reaction is not sufficiently suppressed when the film thickness is 1 μm. But,
When the film thickness was 3 μm or more, the accuracy of the resist pattern dimension was improved and the variation was suppressed to a small value.

[0012]

According to the present invention, the electrochemical reaction due to the formation of local cells on the metal surface of the copper lead frame material and dichromate ions in the water-based resist is suppressed, and the resolution of the resist pattern is improved. In addition, it is possible to eliminate the variation in quality due to the difference in the type of copper alloy, and it is possible to cope with the super-high pin count of the lead frame.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the present invention. FIG. 1 (a) shows a change in resist pattern dimension with respect to the copper plating film thickness.
(B) is a figure which shows the change of the resist pattern dimension variation with respect to a copper plating film thickness.

Claims (2)

[Claims] 1. A method of forming a desired resist pattern using an aqueous photosensitive solution such as casein or PVA containing a dichromic acid-based photosensitizer as an etching resist for a lead frame material made of a copper alloy, and then performing etching. A method for manufacturing a lead frame, characterized in that a copper plating layer is formed on the surface of a copper alloy before the photosensitive solution coating step. 2. The method for manufacturing a lead frame according to claim 1, wherein the thickness of the copper plating layer is 3 μm or more.