JPH043491A - Plating method of circuit or lead frame - Google Patents

Abstract

PURPOSE:To prevent the corrosion of the root of a lead or the end section of a solder resist by plating a circuit or a lead frame with one kind or two kinds or more of metals having standard electrode potential less than the standard electrode potential of copper, forming a solder resist film, and plating the upper section of the circuit or lead frame except said film section with tin or a tin alloy. CONSTITUTION:It is favorable that plating is conducted in approximately the half of the thickness of plating finally required for the section or film thickness of 0.2-0.4mum or less before a solder-resist film is formed. Either one kind of a metal of a metal, which has standard electrode potential less than +0.337V at a value in an aqueous solution, such as tin, lead, zinc, indium, antimony or bismuth or metals consisting of the combination of these two kinds or more or alloy plating, etc., in which other metals are added to these metals and alloys, are employed for first plating. The printing, etc., of a solder resist are performed. The upper section of a previously plated circuit or lead frame, on which the film of the solder resist is not formed, is plated with tin or the alloy or the like.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for plating circuits or lead frames, and in particular, to mounting and bonding of semiconductor devices and semiconductor chips, such as printed circuit boards and tape carriers. This invention relates to a method of plating tin or the like on a circuit or lead frame other than the solder resist coating.

[Prior Art] When a semiconductor device is mounted at a predetermined position on a printed circuit board, the lead frame of the semiconductor device and the circuit of the printed circuit board are usually connected by solder. In this case, in order to improve soldering properties, the circuit portion of this connection portion of the printed circuit board is plated with tin or the like. Also,
Recently, TAB (Tape Auto), a type of tape carrier that mounts a semiconductor chip by forming a lead frame with copper foil on an insulating resin film such as polyimide, has been introduced.
mated bonding) method has begun to be put into practical use. In this method, the bumps of the semiconductor chip and one end of the lead frame on the film are bonded by thermocompression bonding, but in order to improve this thermocompression bonding property, and the other end of the lead frame is used for soldering. In order to improve the soldering process, both ends of the lead frame are plated with tin or the like.

Conventionally, such plating has been performed after forming a solder resist film to prevent solder from adhering to other parts.

Furthermore, the plating bath such as tin for performing this plating is
Based on strong acids such as hydrochloric acid or fluoroboric acid,
Those containing thiourea, divalent tin, etc. were used. However, these baths contain substances that corrode copper or copper alloy materials, such as thiourea, and T
The width of the leads used in the AB method is extremely fine, less than 50 μm, so the base of the lead, which is the contact boundary between the lead and a substrate such as a film, or the edge of the solder resist, which is the contact boundary between the solder resist and the lead, is There was a problem in that it corroded and the leads were likely to break.

Therefore, in order to prevent corrosion at the base of this lead,
An electroless plating bath using an organic sulfonic acid instead of the strong acid used in conventional tin plating baths was proposed (Japanese Patent Application Laid-open No.
3-230883, JP-A-1-184279).

However, this bath was unable to prevent corrosion at the edges of the solder resist.

[Problem to be Solved by the Invention 1] The present invention has been made to solve the above problems, and its purpose is to provide a plating method that does not cause corrosion at the base of the lead or at the end of the solder resist. It's about doing.

[Means for Solving the Problems] The present invention provides a method for plating a circuit or lead frame other than the solder resist coating portion of a circuit or lead frame having a solder resist coating portion, in which, before forming the solder resist coating, , after plating the whole or a part of the circuit or lead frame with one or more metals selected from metals having a standard electrode potential lower than the standard electrode potential of copper, a solder resist film is formed. Then, the circuit or lead frame other than the solder resist coating part is plated with tin or a tin alloy, and it is particularly preferable that the metal having a standard electrode potential lower than the standard electrode potential of the plate is tin, raw metal, etc. , aene, antimony, bismuth, or indium.

The present invention is suitable for circuits made of copper and copper alloys such as printed circuit boards and flexible printed circuit boards, lead frames made of copper and copper alloys such as flat bags, chip carriers, and tape carriers.

The solder resist referred to in the present invention is also called a permanent resist, but it is a protective film to prevent solder from adhering to areas other than the intended part, and is generally made of epoxy resin or acrylate resin. , a resist film is formed using urethane resin or the like.

It is preferable that the plating performed before forming the solder resist film of the present invention has a film thickness of 172 mm or less, which is the thickness at which the final number plating is required for the part concerned. 17
This is because if the thickness is 2 or more, there is a risk of insulation failure between the circuit and the lead frame. The film thickness required for plating cannot be determined generally, as it varies depending on the spacing between each circuit and each lead frame, purpose, application, etc., but is generally set to be approximately 0.4 to 8 μm. Therefore, it is preferable that the initial plating has a thickness of 0.2 to 4 μm or less. The film thickness of this first plating is
If it is less than 0.1 μm, the effects of the present invention cannot be fully exhibited, which is not very preferable.

This initial plating can be performed using the same method as conventional plating, that is, electroplating or chemical plating, but due to ease of operation, chemical plating, especially displacement plating, is used. It is preferable.

This initial plating uses a metal below the standard electrode potential of copper. The standard electrode potential referred to here is the value in an aqueous solution,
The standard electrode potential of copper is +0.337V, and a metal having a standard electrode potential below this value is used. When plating a metal with a standard electrode potential higher than this,
Tin or tin alloy plating in the subsequent process is not uniformly formed. Examples of metals whose standard electrode potential in this aqueous solution is less than +0.337V include tin, sulfur, aene, indium, antimony, bismuth, etc., and any one of these metals or a combination of two or more of these metals can be used. Further, alloy plating can be made by adding other metals to these metals or alloys. There is no particular problem in the initial plating as long as any of the above metals or the total amount of the above metals is 50% by weight or more, and the alloy composition is not particularly problematic.

Further, this initial plating may be performed over the entire circuit or lead frame, or may be performed on a portion thereof. If it is applied to a portion, it includes the portion to be plated in a subsequent process and also includes a portion of the portion covered with the solder resist.

This is natural for the purpose of preventing corrosion at the boundaries of the solder resist film.

Next, a solder resist is printed, and conventional methods such as screen printing can be applied as is.

Thereafter, plating with tin, tin alloy, or the like is performed on the previously plated circuit or lead frame on which the solder resist film was not formed. For this plating, any conventional method such as electrolytic plating or chemical plating can be used. In particular, chemical plating methods using conventional hydrochloric acid or fluoroboric acid-based plating baths containing tin or tin alloys containing thiourea, etc., and organic sulfonic acid-based plating baths are preferably employed. Shitsuru [Example] (Example 1) A comb-shaped pattern (number of bins: 400) with a line and space of 50 μm was formed on a 5.5 CIT 1 square copper-clad glass epoxy laminate. Each of the substrates was immersed in the plating bath shown in Table 1 at the temperature and time shown in the same table to plate the entire pattern to a plating film thickness of 0.2 μm.

Apply solder resist (Nippon Gosei Kagaku, Epoglaze N
-506KG) was printed and heat-cured (130°C, 60 minutes). Thereafter, the pattern was immersed in a tin plating bath having the bath composition shown in Table 2 at a temperature of 70°C for 5 minutes to form a film with a thickness of 0.
Tin plating was performed to a thickness of 7 μm. When the cross-sections of the patterns of these substrates were observed, no abnormality such as corrosion was observed at the edges of the solder resist.

Further, these substrates were heated at 80° C. for 3 hours, and then exposed to an environment of 22° C. and 60% relative humidity for 168 hours. As a result, no abnormalities such as the formation of tin whiskers were observed on any of the substrates.

(The following is a blank space) Table 2 Tin plating bath (unit: g) (Example 2) An electrolytic copper foil was attached to a polyimide tape having a width of 3 cm and having square (lcnl) holes every 3 cm using an epoxy adhesive. Line and space 50μm on this tape
A comb-shaped pattern (160 bins) with a pin tip of 2 m.
It was formed to protrude into the m hole. This tape was immersed in the plating bath shown in Table 1 at the bath temperature and time shown in the same table, and the entire pattern was plated to a film thickness of 0.2 μm. A solder resist (Evoglaze N-504JG, manufactured by Nippon Gosei Kagaku) was printed on the pattern after plating except for the area outside 1 ml Tl from the four sides of the upper hole of the polyimide tape, and was cured by heating (130° C., 60 minutes). Thereafter, it was immersed in the tin plating bath shown in Table 2 at a liquid temperature of 70° C. for 5 minutes to plate the pattern with tin to a thickness of 0.7 μm. When the cross section of this pattern was observed, no abnormalities such as corrosion were observed at the bases of the leads and the ends of the solder resist. In addition, these tapes were heated at 80°C for 3 hours,
Then, at a temperature of 22°C and an environment of 60% relative humidity,
Exposure was made for 68 hours. As a result, no abnormalities such as the formation of tin whiskers were observed on any of the substrates.

(Example 3) The tape used in Example 2 was placed in the plating bath shown in Table 2 at a liquid temperature of 40°C.
℃ for 5 minutes, and the entire pattern was coated with a film thickness of 0.2μ.
I looked at m. A τ solder resist was printed on this and cured by heating. After that, it was immersed in the tin plating bath shown in Table 3 at a liquid temperature of 80℃ for 5 minutes to form a film with a thickness of 0.7μm on the pattern.
It was tin-plated to make it look like this. When the cross section of this pattern was observed, no abnormalities such as corrosion were observed at the bases of the leads and the ends of the solder resist. These tapes were also heated at 80° C. for 3 hours and then exposed to a temperature of 22° C. and a relative humidity of 60% for 168 hours.

As a result, no abnormalities such as the formation of tin whiskers were observed on any of the substrates.

(Comparative Example 1) A solder resist was printed on the substrate used in Example 1 without plating the entire pattern, and was cured by heating. After that, it was immersed in the plating bath shown in Table 2 for 5 minutes at a liquid temperature of 70°C.
Tin plating with a film thickness of 0.7 μm was performed on the pattern. When the cross section of this pattern was observed, corrosion with a depth of 4 μm was observed at the end of the solder resist.

(Comparative Example 2) A solder resist was printed on the tape used in Example 2 without plating the entire pattern, and the tape was cured by heating. Thereafter, it was immersed in the tin plating bath shown in Table 2 at a liquid temperature of 70'C for 5 minutes to plate the pattern with tin to a film thickness of 0.7 μm. When we observed the cross section of this pattern, we found that there was a depth of 2μ at the base of the lead and at the end of the solder resist.
Corrosion of m and 4 μm was observed.

(Comparative Example 3) A solder resist was printed on the tape used in Example 2 without plating the entire pattern, and the tape was cured by heating. Thereafter, it was immersed in the tin plating bath shown in Table 3 at a liquid temperature of 80° C. for 5 minutes to plate the pattern with tin to a film thickness of 0.7 μm. When the cross section of this pattern was observed, corrosion with a depth of 6 μm was observed at the end of the solder resist.

[Effects of the Invention] As explained above, the plating method according to the present invention has a special effect on preventing corrosion of the base of the lead or the end of the solder resist, which occurs during the plating process of tin, etc. of a circuit or lead frame. This is particularly effective in cases where the lead width of a TAB or the like is extremely narrow and lead corrosion can cause fatal damage to the product.

Claims (2)

[Claims] (1) In a method of plating a circuit or lead frame other than the solder resist coated part of a circuit or lead frame having a solder resist coat, before forming the solder resist coat, the entire circuit or lead frame or After plating a part with one or more metals selected from metals having a standard electrode potential lower than the standard electrode potential of copper, a solder resist film is formed, and then the circuits other than the solder resist film part are plated. Or a method for plating a circuit or lead frame, which comprises plating the lead frame with tin or a tin alloy. (2) A method for plating a circuit or lead frame, characterized in that the metal having a standard electrode potential lower than the standard electrode potential of copper according to claim (1) is tin, namali, aene, antimony, bismuth, or indium.