JPS6250476A - Method for plating nickel-boron alloy - Google Patents

Abstract

PURPOSE:To form an Ni-B alloy film having superior heat resistance an solderability by carrying out electroplating at a low temp. with a soln. prepd. by using a borohydride compound as a reducing agent in an electroless Ni plating bath having a prescribed composition. CONSTITUTION:A borohydride compound as a reducing agent is added to a soln. contg. an Ni salt and an org. acid such as citric acid, malonic acid or tartaric acid or a salt thereof as a complexing agent to prepare an electroless Ni plating soln. Electroplating is carried out with the plating soln. kept at such a low temp. as about 50 deg.C at which an electroless plating reaction slightly takes place or does not take place at all. By the electroplating, a metallic Ni film is deposited and simultaneously a very small amount of B is deposited. A metallic film formed by this method has heat resistance and solderability comparable to those of an Ni-B alloy film formed by conventional electroless plating. The plating time is shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a nickel-boron alloy plating method.

(Prior art and its problems) Conventional nickel-boron alloy plating is performed exclusively by electroless plating. However, this electroless plating requires a long plating time of about 10 minutes to obtain a film thickness of about 1 μm. Therefore, it is difficult to continuously apply plating including electrolytic plating of gold, silver, etc. and electroless plating of nickel-boron alloy to a long object such as a lead frame used for a semiconductor device in the same plating line. While plating takes a short time, electroless plating takes a long time as mentioned above, so the difference between the two is too large, and the electroless plating bath is unstable and has a short bath life. It was impossible.

The background why such nickel-boron alloy plating and electrolytic plating of gold, silver, etc. have become necessary will be explained with regard to lead frames.

An example of an assembly process for a resin-sealed semiconductor device is as follows.

■A gold or silver plating layer is formed on the stage part and internal lead part of the lead frame by partial electrolytic plating.

(2) Fixing the semiconductor element to the stage part using a gold-silicon eutectic alloy or the like.

■Perform wire bonding between the semiconductor element and internal leads.

■Mold the resin sealing area including the semiconductor element mounting area with resin.

■Apply tin or solder plating, or solder immersion treatment to the external leads.

In each of the above steps, the step (2) of subjecting the external lead portion to tin or solder plating or solder immersion treatment poses a technical problem.

In other words, when performing plating using tin or solder plating, it naturally goes through a wet process in which it is immersed in a pretreatment solution or plating solution, so there is a problem in that the reliability of semiconductor elements decreases due to moisture. There is.

When performing solder immersion treatment, it is necessary to remove metal oxide films that have formed on the external leads due to heat history during semiconductor element fixing and wire bonding, so use flux with a high halogen value. There is a need.

The halogen ions generated at this time may damage the wiring circuit made of aluminum or the like of the semiconductor element, which again poses the problem of lowering the reliability of the semiconductor element.

In order to deal with the above problems, a method has been proposed in which a tin or solder film is formed on the lead frame in advance. However, when using this method, subsequent semiconductor elements are The thermal history during fixing, wire bonding, and resin molding is kept to a maximum of 200℃ or less.However, the tin or solder film changes color (oxidation) during this thermal process, reducing the solderability of the product. There is.

As a result of intensive studies in view of the various problems mentioned above, the inventor noticed that the nickel-boron alloy plating film has excellent heat resistance and soldering properties. It has been found that by applying a nickel-boron alloy plating film to the nickel-boron alloy, all of the above-mentioned problems such as moisture, flux, and the temperature limit of 200° C. or less during assembly can be solved.

However, in the past, this nickel-boron alloy plating has only been carried out electrolessly, which has led to the aforementioned manufacturing problems.

(Summary of the Invention) The present invention has been made to solve the above-mentioned manufacturing problems, and its objectives are 2. On the same plating line as the necessary electrolytic plating of gold, silver, etc., It is an object of the present invention to provide a nickel-boron alloy plating method capable of performing nickel-boron alloy plating.

However, its characteristics are that it uses an electroless nickel plating solution in which a borohydride compound is added as a reducing agent to a solution containing a nickel salt and an organic acid such as citric acid, malonic acid, or tartaric acid or a salt thereof as a complexing agent; Electroless plating involves performing electrolytic plating under temperature conditions where little or no reaction occurs.

(Function) Boron hydride compounds act as strong reducing agents for nickel ions. In normal electroless plating, a boron hydride compound self-decomposes on the plated surface where it has catalytic activity under relatively high temperature conditions, and at the same time, nickel ions are reduced and deposited as metallic nickel on the material.

Further, at this time, boron is incorporated into the metal nickel, albeit in a small amount, and a plating film is formed as a nickel-boron alloy. This nickel-boron alloy film has much better heat resistance stability and solderability than a simple nickel film.

In the present invention, the bath temperature is set to 50°C, which is a temperature condition where electroless plating reaction occurs slightly or not at all.
The electrolytic plating process is performed under low-temperature conditions, around ℃. As a result, it was confirmed that although no metal film was deposited under non-electrolytic conditions, a metal nickel film was deposited by this energization, and at the same time a trace amount of boron was eutectoid. In this case, the current density is IA/dr! Good metal film deposition was obtained at low current densities before and after. this is,
It is thought that this is because the electrical potential of the plating surface reached a level at which the electroless metal deposition reaction simultaneously proceeded when nickel was deposited due to the application of electricity.

In this way, it was confirmed that the obtained metal film was not a pure nickel film, but had excellent heat resistance and solderability comparable to conventional electroless nickel-boron alloy plating films, and electroless The problems of bath instability and short life, which are drawbacks of plating, have been solved.

In other words, compared to conventional simple electroless plating, self-decomposition of the boron hydride compound can be suppressed by controlling the bath temperature to a certain low temperature, and most of it is consumed in proportion to the amount of electricity applied. Therefore, the bath composition control conditions that must be considered in the case of electroless plating can be ignored, and it can be replenished according to the amount consumed in the same way as gold and silver in the case of ordinary gold and silver plating baths. I can do it. by this,
This makes it possible to incorporate nickel-boron alloy plating into regular electrolytic plating lines.

The borohydride compound is potassium borohydride KBI+
, , boron compounds such as sodium borohydride NaBH (c, methylamine borane CHjN H, B I+,
, ethylamine borane (C2H,) NH,BH,, dimethylamine borane (C) I, ), NHBII, ,
Diethylamineborane (C2H,)2NHBH, )dimethylamineborane (CIIJ).

NBH,, triethylamine borane (C7H,), N
Amine-adducted borohydride compounds such as BII, Me, etc. can be used.

Note that dimethylamine borane (CI+), NHBFI, and the like are suitable for use at a low bath temperature of about 40°C to 60°C.

Moreover, as the methyl group and the ethyl group mentioned above, a propyl group-added borohydride compound can also be used.

In addition, the inventor has developed a conventional electrolytic nickel plating bath.
It has been found that a nickel-boron alloy plating film can also be obtained by adding the above-mentioned amine-added borohydride compound as a reducing agent to a Watt nickel plating bath or a sulfamine nickel plating bath under low temperature and electric current conditions.

(Example) An example of application to a lead frame for semiconductor packaging is shown below.

FIG. 1 shows a lead frame 10 used in a resin-sealed semiconductor device.

In the figure, reference numeral 12 denotes a stage portion, which is plated with gold or silver, and is a portion to which a semiconductor element is fixed using a gold-silicon eutectic alloy or the like.

Reference numeral 14 denotes an internal lead part provided surrounding the stage part 12, the tip of which is similarly plated with gold or silver, and connected to the semiconductor element mounted on the stage part 12 by a wire.

Reference numeral 16 is an outer lead portion following the inner lead portion 14, and is plated with a nickel-boron alloy as described later.

18 is a dam bar, which dams the resin.

20 is an outer frame.

The area indicated by the broken line in the figure is the resin mold area.

What is shown in FIGS. 2 to 4 are various examples showing the type of plating and the coverage area of the plating.

In the case shown in FIG. 2, a nickel plating film 22 is formed over the entire range of the lead frame 10, and the stage portion 1
2 and the tips of the internal lead portions 14 are partially plated with a silver plating film (or gold plating film) 24. A nickel-boron alloy plating film 26 is formed on the nickel plating film 22 on the external lead portion 16.

The one shown in FIG. 3 has a silver plating film (or gold plating film) 2 on the stage part 12 and internal lead part 14 tips
4 is partially plated, and nickel is applied on the external lead portion 16 slightly extending into the resin mold area (dashed line).
The boron alloy plating film 26 is partially plated.

In the case shown in FIG. 4, a nickel-boron alloy plating film 26 is formed over the entire lead frame 12, and silver plating is further applied on the nickel-boron alloy plating film 26 at the tips of the stage section 12 and internal lead section 14. Film (
Alternatively, the gold plating film 24 is partially plated.

Since the nickel-boron alloy plating film 26 has excellent heat resistance, it can be used in the subsequent steps, that is, when the semiconductor element is fixed to the stage part 12'' by the gold-silicon eutectic alloy, and this The nickel-boron alloy plating film 26 is extremely stable even after the heat history during wire bonding between the semiconductor element and the tip of the internal lead portion 14 and the heat history during resin molding, and a metal oxide film is not formed. There isn't.

Therefore, in conventional soldering, the oxide film removal process as a pre-treatment is completely unnecessary, and the problem of lower reliability of semiconductor elements caused by a wet process can be solved.

Furthermore, the solder leakage to the nickel-boron alloy plating film 26 is extremely good. Therefore, pre-treatment flux treatment is not completely unnecessary for soldering, but instead of using conventional flux with a high halogen value,
A flux with a low halogen value can be used, and the adverse effects of halogen ions on semiconductor elements can be suppressed to the utmost.

Example 1 Nickel sulfate 30 g/l Sodium malonate 35 g/β dimethylamine borane 3.4 g/J thallium nitrate
0.1 g/ff pH 6.5 Bath temperature 50°C Using the above plating bath, a current density IA/d rI was applied to the external lead part of the 42 alloy lead frame (other parts were masked) at a low temperature of around 50°C. A 0.1 μm thick nickel-boron alloy plating film with excellent heat resistance and soldering properties was obtained.

The stage part and internal lead parts are partially plated with copper strike plating, and then silver plating is applied on top of that.

Example 2 Nickel chloride 30g/j2 Potassium citrate 60g//Ammonium chloride
30g/jl! dimethylamine borane
5.0 g/βP1 (9 Bath temperature: 40°C) Using the above plating bath, masking the stage part and internal lead part, apply a current density of 0.05 μm to the external lead part of the 42 alloy lead frame at a current density of 2 A/d m. The time required for this was approximately 8 seconds.After that, the stage part and the internal lead part were plated with grooves, and then a 5 μm thick plating was applied on top of that.
Silver plated. The time required for this was approximately 5 seconds.

Example 3 Nickel sulfate 20 g/β potassium sodium tartrate 40 g/ffi Sodium borohydride 2 g/IPH13 Bath temperature 40°C Using the above plating bath, the stage part and internal lead part were masked and the outside of the lead frame made of prepared alloy was masked. Current density 2A/dn in the lead part? 0.1 μm plating was applied.

The time required for this was approximately 15 seconds.

Thereafter, 1 μm gold plating was applied to the stage portion and internal lead portions. The time required for this was approximately 10 seconds.

By performing electrolytic plating using an electroless nickel plating solution containing a boron hydride compound in this way,
A lead frame was obtained in which the external lead part was plated with a nickel-boron alloy that had excellent heat resistance and soldering properties, and the stage part and the internal lead part were plated with ordinary silver or gold.

Example 4 Nickel sulfate 300 g/l Nickel chloride 40 g/! ! Boric acid
40g/l trimethylamine borane
0.5g/l sodium thioglycolate 10
ppmPH5,5 Bath temperature 45°C The stage part and internal lead part were masked using a plating bath in which trimethylamine borane was added as a boron hydride compound to the above conventional Watt nickel plating bath, and the external lead part of the lead frame made of prepared alloy was masked. 0.1 μm plating was applied at a current density of 5.04/d rrr. The time required for this was about 6 seconds, and a nickel-boron alloy plating film with excellent heat resistance and solderability was obtained.

Copper strike plating was applied to the stage part and internal lead part, and 6 μm silver plating was applied thereon. The time required for this was approximately 6 seconds.

Example 5 Nickel sulfamate 400 g/l Nickel bromide 5 g/l boric acid
40g71 Methylmorpholineborane
5g/lP-iodoaniline 1p
pm PH 5,5 Bath temperature 40° C. The stage portion and the interior were retouched using a plating bath in which methylmorpholine borane was added as a boron hydride compound to the above sulfamine nickel plating bath. The time required for this was about 8 seconds, and a nickel-boron alloy plating film with excellent heat resistance and solderability was obtained. The internal lead portion and the stage portion were plated with 1 μm gold. The time required for this was approximately 10 seconds.

In this way, electrolytic plating is performed using a Watt nickel plating bath, a sulfamine nickel plating bath, and a plating bath in which an amine-added boron hydride compound is added. A lead frame having a nickel-boron alloy plating film could be obtained.

As shown in Examples 4 and 5, an amine-added borohydride compound, which is more stable than the reducing agent used in the electroless plating bath described above, was added to the Watt nickel plating bath and the sulfamine nickel plating bath, and the borohydride compound was added to the Watt nickel plating bath and the sulfamine nickel plating bath. By plating, a good nickel-boron alloy plating film was obtained. In addition, it has been confirmed that this bath is fully usable for the mechanical mask method, which is often used as a partial plating method. It was confirmed that this method is extremely effective in manufacturing lead frames that have a partial nickel-boron alloy plating film on the outer lead portion.

(Effects of the Invention) As described above, according to the present invention, electrolytic plating of nickel-boron alloy plating can be applied, for example, when nickel-boron alloy plating is applied together with other electrolytic plating such as gold or silver plating. In addition, nickel-boron alloy plating can be incorporated into the same plating line as other electrolytic plating, making it possible to perform high-speed continuous plating processing such as a reel-to-reel method.

In addition, not only can a plating film with excellent heat resistance and solderability fully comparable to nickel-boron alloy plating films obtained by electroless plating be obtained, but the plating time is significantly reduced compared to electroless plating. It has a number of significant effects, including the ability to improve

Although the present invention has been variously explained above with reference to preferred embodiments, the present invention is not limited to these embodiments, and it goes without saying that many modifications can be made without departing from the spirit of the invention. It is.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a lead frame, and FIGS. 2 to 4 are cross-sectional explanatory diagrams showing various embodiments showing the types of plating and the coverage thereof. 10... Lead frame, 12... Stage part, 14... Internal lead part,
16... External lead part, 18... Dam bar,
20...Outer tL 22...Nickel plating film, 24...Silver plating film (gold plating film), 26
...Nickel-boron alloy plating film.

Claims (1)

[Claims] 1. Using an electroless nickel plating solution in which a borohydride compound is added as a reducing agent to a solution containing a nickel salt and an organic acid such as citric acid, malonic acid, or tartaric acid or a salt thereof as a complexing agent. A nickel-boron alloy plating method characterized in that electrolytic plating is carried out under temperature conditions at which little or no electroless plating reaction occurs. 2. The nickel-boron alloy plating method according to claim 1, wherein the borohydride compound is an amine-added borohydride compound. 3. A nickel-boron alloy plating method characterized in that electrolytic plating is performed using a plating solution in which an amine-added borohydride compound is added to a Watt nickel plating bath or a sulfamine nickel plating bath.