JPH11186618A - Pre-plating method for thermoelectric semiconductor - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To shorten the steps in a pretreatment method for plating a thermoelectric semiconductor. SOLUTION: In the pretreatment method for plating a thermoelectric semiconductor, the thermoelectric semiconductor is electrolytically etched in an alkaline solution. Since the alkaline solution itself has a degreasing effect of removing organic stains, the thermoelectric semiconductor is electrolytically etched to form irregularities on its surface, and is also degreased. For this reason, it is not necessary to perform degreasing before etching, and the plating pretreatment step can be shortened as compared with a conventional pretreatment method that requires degreasing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pretreatment method for plating a thermoelectric semiconductor.

[0002]

2. Description of the Related Art A thermoelectric converter utilizes a Peltier effect in which thermoelectric elements made of different types of conductors or semiconductors are electrically connected and energized to generate or absorb heat other than Joule heat at their contacts. The generated cold or warm heat is used for various purposes. As a thermoelectric element used in such a thermoelectric conversion device, a thermoelectric semiconductor is often used in terms of thermoelectric power. As an example of the thermoelectric semiconductor, there is a thermoelectric semiconductor mainly composed of an intermetallic compound such as a bismuth-tellurium-based, antimony-tellurium-based, Pb-Ge-based, or silicon-Ge-based.

[0003] A thermoelectric semiconductor used in a thermoelectric converter may have a plating film formed on its surface for various purposes such as surface smoothing, improvement of bonding strength, and suppression of quality performance deterioration. For example, when connecting a thermoelectric semiconductor to an electrode made of copper or the like formed on a substrate by soldering, to prevent the tin component of the solder from diffusing into the thermoelectric semiconductor and deteriorating the quality performance, and In order to ensure the wettability of the solder, it is necessary to form a plating film for solder bonding.

When coating a thermoelectric semiconductor with plating, the adhesion between the thermoelectric semiconductor and the plating film must be considered in order to ensure the durability of the thermoelectric conversion device. , Plating pretreatment.

[0005] In the conventional plating pretreatment, a degreasing treatment for removing foreign substances and organic dirt attached to the surface of the thermoelectric semiconductor is performed, and after washing and neutralization, an acid is formed to form irregularities on the surface of the thermoelectric semiconductor. An etching treatment (acid etching) is performed in a solution, and an acid treatment for activating the surface while removing inorganic dirt such as an oxide film, scale, and smut attached to the surface of the thermoelectric semiconductor as necessary. . The irregularities formed on the surface of the thermoelectric semiconductor during the etching process have a function of improving the adhesion between the thermoelectric semiconductor and the plating film by causing plating to enter the irregular surface and generating an anchor effect.

[0006]

However, in the above-described prior art plating pretreatment, at least two steps of etching and degreasing are required, and there are many processing steps in addition to other washing and neutralization. There's a problem.

[0007] Further, in the conventional acid etching, bismuth and tellurium of the thermoelectric semiconductor material are specified and dissolved, so that the composition of the thermoelectric semiconductor material changes. As a result, there is a problem that the surface portion exposed to the etchant becomes a damaged layer, and deteriorates semiconductor performance.

Further, there is a problem that the etching processing time is long and the productivity is poor.

[0009] Therefore, the present invention has been made in view of the above-mentioned circumstances, and in a method for pre-treating a thermoelectric semiconductor, it is intended to reduce the number of processing steps, maintain semiconductor performance in pre-treatment, and improve productivity. This is a technical issue.

[0010]

According to a first aspect of the present invention, there is provided a method for pre-plating a thermoelectric semiconductor, comprising: electrolytically etching a thermoelectric semiconductor in an electrolyte solution. It was that.

According to the invention, as the pretreatment for plating the thermoelectric semiconductor, the thermoelectric semiconductor is electrolytically etched in the electrolyte solution. Electrolytic etching forms irregularities on the surface of the thermoelectric semiconductor in order to secure adhesion to the plating film by an anchor effect, and also has a degreasing action for removing organic dirt. Therefore, by performing the electrolytic etching of the thermoelectric semiconductor in the electrolyte solution, the formation of the unevenness on the surface of the thermoelectric semiconductor and the degreasing are simultaneously performed.

Therefore, it is not necessary to perform degreasing before etching, and the plating pretreatment step can be shortened.

In addition, since electrolytic etching uniformly dissolves a metal in a thermoelectric semiconductor material, irregularities can be formed on the surface without causing composition damage as compared with dissolution of a specific element such as acid etching. For this reason, the performance of the thermoelectric semiconductor can be maintained.

In addition, the electrolytic etching requires a very short processing time as compared with the conventional acid etching. Therefore,
The processing time can be shortened and the productivity can be improved.

[0015] In order to solve the above technical problems by the invention of claim 1, it is preferable that the electrolyte solution is a sodium hydroxide solution as in the invention of claim 2.

As the electrolyte solution, a sodium carbonate salt solution,
Examples thereof include a sodium phosphate salt solution and a sodium hydroxide solution. Use of a sodium hydroxide solution having a very strong saponification effect as in the present invention improves the degreasing effect.

More preferably, the concentration of the sodium hydroxide solution is 10 to 100.
g / l. When the concentration is within the above range, it is possible to apply a high current in electrolytic etching. Also,
When the concentration is out of the above range, not only is it difficult to apply a high current in electrolytic etching, but also the viscosity of the liquid becomes high, so that it takes time to drain the liquid at the end of electrolytic etching.

Further, in solving the above technical problems by the inventions of claims 1 to 3, as in the invention of claim 4, the electrolytic etching is carried out by a pairwise reverse (p
It is preferable to use an erodic reverse electrolytic etching (hereinafter, PR electrolytic etching) or an anodic electrolytic etching.

When the electrolytic etching is performed by PR electrolytic etching or anodic electrolytic etching, the base metal is eluted on the anode side, and uniform and fine irregularities are formed. Therefore, uniform plating is performed in a later plating step. can do. Further, by performing the PR electrolytic etching, the non-conductive film is activated on the cathode side, and a more effective etching action can be performed at a high speed.

The PR electrolytic etching is a method in which an anode and a cathode are alternately reversed to perform electrolytic etching. The anodic electrolytic etching is a method in which electrolytic etching is performed using a member to be etched as an anode. is there.

Further, in solving the above technical problem by the invention of claim 1, as in the invention of claim 5, the thermoelectric semiconductor is subjected to the acid etching after the electrolytic etching in the electrolyte solution. Is preferred.

According to this, the surface of the thermoelectric semiconductor is activated by performing the acid treatment after the electrolytic etching, and the plating adhered to the activated surface is bonded to the thermoelectric semiconductor and metal on the surface. Therefore, in addition to the anchor effect due to the surface irregularities formed by the etching treatment, the adhesion between the thermoelectric semiconductor and the plating film is further improved by the intermetallic bonding between the thermoelectric semiconductor and the plating film.

Usually, the improvement of the adhesion due to the anchor effect is proportional to the size of the surface roughness of the thermoelectric semiconductor surface (the size of the surface irregularities) due to the etching treatment, and the surface roughness is large.
That is, the rougher the surface, the better the adhesion. However, it has been found that the cooling performance deteriorates as the surface roughness of the thermoelectric semiconductor increases. On the other hand, in the present invention, it is possible to improve adhesion by bonding between the thermoelectric semiconductor and the plating film, so that sufficient adhesion can be obtained without increasing the surface roughness of the thermoelectric semiconductor. In addition, it is possible to maintain both the cooling performance of the thermoelectric semiconductor and the improvement of the adhesion. In addition, since the surface roughness of the thermoelectric semiconductor surface does not need to be so large, the etching time can be shortened.

More preferably, as in the invention of claim 6, the acid activation treatment is a mixed solution of sulfuric acid having a concentration of 400 to 500 ml / l and an aqueous solution of hydrogen peroxide having a concentration of 10 to 50 ml / l. The processing time is 0.5 to 2 minutes.

According to this, by setting the treatment conditions in the acid activation treatment as described above, activation and oxidation of the inactive film by acid, and removal of scale and smut by generated oxygen are performed.

[0026]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 shows a first embodiment of the present invention.
It is the schematic of the plating pre-processing apparatus in the plating pre-processing process in embodiment. In the figure, reference numeral 1 denotes a pretreatment tank, and the concentration of the electrolyte solution in the pretreatment tank 1 is 40 g / l.
Contains sodium hydroxide solution. In the pretreatment tank 1, two electrodes 2, 3 are arranged so that most of them are immersed in a sodium hydroxide aqueous solution. Both electrodes 2 and 3 are composed of insoluble electrodes, for example, carbon or platinum electrodes. A pallet 4 is further disposed in the pretreatment tank 1 in a state of being immersed in an aqueous solution of sodium hydroxide.
Within the pallet 4, a plurality of thermoelectric semiconductors 5 formed in a plate shape are arranged in a stacked state.

FIG. 2 is a view showing the pallet 4 on which the thermoelectric semiconductors 5 are placed. In the figure, the pallet 4 includes a bottom plate 4 a as a contact electrode and a holding portion 4 b for holding the thermoelectric semiconductor 5. The holding portion 4b is formed by arranging two flat plates having a shape in which unevenness is repeated as is apparent from the figure, and inserts and accommodates the thermoelectric semiconductor 5 in a space portion that is long in the width direction. .

In FIG. 1, the power source 6 is provided with two output terminals, and one output terminal has a first lead wire 7a.
However, a second lead wire 7b is connected to the other output terminal. The first lead wire 7a branches on the way, and each branched lead wire is connected to the electrode 2 and the electrode 3, respectively. The second lead wire 7b also branches midway, and the branched lead wires are connected to both ends of the pallet 4, respectively. The plurality of thermoelectric semiconductors 5 placed on the pallet 4 are electrically connected to the second lead wire 7b via the bottom plate 4a and the holding portion 4b of the pallet 4. Therefore, the electrode 2 connected to one output terminal of the power supply 6 via the first lead wire 7a
And 3 are simultaneously applied to one of the electrodes, which simultaneously serves as a cathode or an anode,
A plurality of thermoelectric semiconductors 5 connected to the other output terminal of the power supply 6 via the second lead wire 7b and the pallet 4 correspond to the other electrode serving as an anode or a cathode in a phase opposite to that of the one electrode. It is.

In the plating pretreatment apparatus having the above structure, P
The thermoelectric semiconductor 5 was etched by R electrolytic etching. The etching conditions are shown below.

Cathode current density 0.5 to 3 A / mm ² Anode current density 0.5 to 3 A / mm ² PR ratio (−: +) 1: 3 1 cycle time 8 seconds Processing time 24 to 60 seconds The current density refers to the current density flowing on the electrode side serving as the cathode, the anode current density refers to the current density flowing on the electrode side serving as the anode, and the PR ratio refers to the case where the thermoelectric semiconductor 5 to be etched is the cathode (-). The time ratio between the time and the time to become the anode (+), one cycle time is the reversal period of the electrode,
The processing time is an electrolytic etching time. By this PR electrolytic etching, the metal forming the thermoelectric semiconductor is uniformly eluted, and irregularities are formed on the surface of the thermoelectric semiconductor. In addition, along with the formation of the unevenness, organic dirt adhering to the thermoelectric semiconductor surface is also removed.

After performing the above-mentioned PR electrolytic etching, the thermoelectric semiconductor 5 is taken out and then subjected to an acid treatment. This acid treatment is performed by immersing in a mixed solution of 98% (410 to 450 ml / l) sulfuric acid and a 35.6% (15 to 25 ml / l) aqueous hydrogen peroxide solution at a bath temperature of 16 to 20 ° C. The processing time was 0.5 to 2 minutes. This acid treatment activates the thermoelectric semiconductor surface.

After performing the above-mentioned acid treatment, neutralization and washing were performed, and thereafter, the thermoelectric semiconductor 5 was placed in a plating bath, and electroless Ni-P plating was performed. In this plating step, Ni-B, Au, Pd plating or the like can be used as electroless plating, and Ni or Au plating can be used as electrolysis. However, inexpensive electroless Ni-P or electrolytic Ni plating is preferable. Hereinafter, the composition of the electroless Ni-P plating bath and the plating treatment conditions of this example are shown below.

Plating bath composition Nickel sulfate 22.5 g / l Sodium hypophosphite 23.85 g / l Lactic acid 27 g / l Sodium succinate 16 g / l Plating treatment conditions pH 4.8 Bath temperature 20-70 ° C. Treatment time 5 The plating film was applied to the thermoelectric semiconductor 5 by the treatment for 30 minutes or more. In this electroless Ni-P plating step, the PR
The plating enters into the irregularities on the surface of the thermoelectric semiconductor formed by the electrolytic etching process, and the thermoelectric semiconductor and the plating adhere to each other by the anchor effect, and the plating between the thermoelectric semiconductor and the plating metal is more firmly formed by the intermetallic bonding between the plating metal and the metal of the thermoelectric semiconductor. Are in close contact with each other.

By the above process, the thermoelectric semiconductor Ni-P
Plated. In the above-mentioned PR electrolytic etching step, the cathode and anode current densities and the processing times are changed within the range of the etching conditions shown above, thereby performing
A plurality of thermoelectric semiconductors 5 having different surface roughnesses were produced, and these were plated under the same conditions as described above.

FIG. 3 shows the surface roughness of each thermoelectric semiconductor in the plated thermoelectric semiconductor manufactured by the above process.
Measure the adhesion and the Seebeck coefficient reduction rate (percentage of the difference between the Seebeck coefficient before and after the plating pretreatment and the Seebeck coefficient after plating), and plot the relationship between the adhesion and the Seebeck coefficient reduction rate on the surface roughness. It is shown. In this case, 0.47 kg / mm ² was taken as the threshold value of the adhesion force that could satisfy the durability of the product. In the figure, the curve shown by the solid line A is a graph showing the relationship between the surface roughness and the adhesion for the one produced in this example, and the curve shown by the dotted line B is the pre-treatment as a comparative example for this example. Is a graph showing the relationship between the surface roughness and the adhesion when etching was performed by hydrochloric acid etching. Incidentally, the straight line indicated by the solid line C is a graph showing the relationship between the surface roughness of the thermoelectric semiconductor and the Seebeck coefficient reduction rate. The Seebeck coefficient reduction rate is due to the surface roughness of the thermoelectric semiconductor, Irrespective of the adhesive strength of the sample, the one in the present example and the one in the comparative example show the same tendency.

As can be seen from FIG. 3, even in the plating pretreatment method according to the present embodiment in which the degreasing treatment is omitted, there is a region where a necessary adhesion force (0.47 kg / mm ² ) is obtained. Therefore, the steps can be shortened by omitting the degreasing treatment.

FIG. 3 shows that in this example, the surface roughness for obtaining the required adhesion (0.47 kg / mm ² ) is 2.0 to 2.5 or more, and in this case, the Seebeck coefficient decreases. The rate is between 3.5 and 4.0%. On the other hand, the comparative example shown by the dotted line in FIG.
The surface roughness for obtaining mm ² ) is 4.7 to 5.0 or more, and the Seebeck coefficient reduction rate at this time is 7.0. Thus, the thermoelectric semiconductor pre-plated by the method of the present example is more than the one pre-plated by the method of the comparative example.
A predetermined adhesive force can be secured with a small surface roughness, and a decrease in the Seebeck coefficient can be suppressed to a small extent.

As described above, in the plating pretreatment method according to the present embodiment, since the thermoelectric semiconductor is electrolytically etched in the electrolyte solution, the thermoelectric semiconductor is etched during the etching step, and at the same time, organic dirt is removed and degreasing is performed. Done.
Therefore, it is not necessary to perform degreasing before etching, and the plating pretreatment step can be shortened.

Further, unlike the specific element dissolution such as acid etching, the metal dissolution of the thermoelectric semiconductor material is uniformly caused, so that the performance of the thermoelectric semiconductor can be maintained.

Further, since the processing time is very short as compared with the conventional acid etching, the processing time can be shortened and the productivity can be improved.

Since the electrolyte solution in the pretreatment tank 1 is a sodium hydroxide solution having a very strong saponifying action,
The degreasing effect is improved.

Further, since the thermoelectric semiconductor is etched by the PR electrolytic etching, the base material is dissolved and the non-conductive film is activated more efficiently.

Further, since the acid treatment is performed after the thermoelectric semiconductor is electrolytically etched, the surface of the thermoelectric semiconductor is activated, and the plating adhered to the activated surface is intermetallically bonded to the thermoelectric semiconductor on the surface. For this reason, in addition to the anchor effect due to the surface irregularities formed by the etching treatment, the adhesion between the thermoelectric semiconductor and the plating film is further improved by the intermetallic bonding. In addition, since the adhesion can be ensured also by the intermetallic bonding, the time for forming concavities and convexities on the thermoelectric semiconductor by electrolytic etching may be completed in a very short time of 24 to 60 seconds as in this example. Therefore, the etching time can be shortened. In this case, since the etching time is short, the irregularities on the thermoelectric semiconductor surface are minute, that is, the surface roughness is relatively small,
It is possible to suppress a decrease in cooling performance due to a large surface roughness. For this reason, it is possible to maintain both the cooling performance of the thermoelectric semiconductor and the improvement of the adhesion.

(Second Embodiment) In the first embodiment described above, the pre-plating process when plating a thermoelectric semiconductor formed in a flat plate shape has been described. Therefore, in order to mount the thermoelectric semiconductor provided with the plating film on the thermoelectric conversion device as described above, it is necessary to further reduce the size of the flat thermoelectric semiconductor into a thermoelectric semiconductor chip. On the other hand, in the present embodiment, a plating pretreatment apparatus for plating a thermoelectric semiconductor in a chip shape in advance will be described.

FIG. 4 shows a plating pretreatment apparatus according to this embodiment. In the figure, reference numeral 1 denotes a pretreatment tank, in which an aqueous solution of sodium hydroxide having a concentration of 40 g / l is contained. In the pretreatment tank 1, two electrodes 2, 3 are arranged so that most of them are immersed in a sodium hydroxide aqueous solution. A barrel 8 is further disposed in the pretreatment tank 1 in a state of being immersed in an aqueous solution of sodium hydroxide. In the barrel 8, a plurality of plates 9 to be plated and an iron ball 10 are formed. They are mixed and housed.

FIG. 5 is an enlarged view of the object 9 to be plated. In the figure, a plated body 9 is composed of a masking body 9a and a thermoelectric semiconductor 9b formed in a chip shape. Only the surface of the thermoelectric semiconductor 9 to be plated is exposed, and the other surfaces are covered by the masking body 9a. Masked.

The other structure is the same as that of the first embodiment, and the description is omitted.

In the plating pretreatment apparatus having the above-described structure, power is supplied from the power supply 6 to perform PR electrolytic etching. At this time, one electrode is the electrode 2 and the electrode 3, and the other electrode is the thermoelectric semiconductor 9 b in the plated body 9 to which current is transmitted from the second lead wire 7 b via the iron ball 10. Therefore, the surface of the thermoelectric semiconductor 9b exposed from the plating object 9 is etched.

The step after the above-mentioned etching treatment is the first
The description is omitted because it is the same as the embodiment.

As described above, in the present embodiment, since the thermoelectric semiconductor chip itself is plated after the pre-plating process, the plated thermoelectric semiconductor chip can be directly mounted on the thermoelectric converter, and the chipping of the thermoelectric semiconductor is omitted. Is what you can do.

[0052]

As described above, according to the present invention, the pre-plating process for thermoelectric semiconductors can be shortened.

[Brief description of the drawings]

FIG. 1 is a schematic view of a plating pretreatment apparatus according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of a pallet on which a thermoelectric semiconductor is placed according to the first embodiment of the present invention.

FIG. 3 is a graph showing the relationship between the surface roughness after plating pretreatment and the adhesion of a plating film and the rate of decrease in the Seebeck coefficient of a thermoelectric semiconductor, together with a comparative example, in the first embodiment of the present invention.

FIG. 4 is a schematic diagram of a plating pretreatment apparatus according to a second embodiment of the present invention.

FIG. 5 is an enlarged view of a body to be plated in a second embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Pretreatment tank 2, 3 ... Electrode 4 ... Pallet, 4a ... Bottom plate, 4b ... Holder 5 ... Thermoelectric semiconductor 6 ... Power supply 7a ... 1st lead Wire 7b Second lead wire 8 Barrel 9 Plated body 9a Masking body 9b
..Thermoelectric semiconductor

Claims (6)

[Claims] 1. A pre-plating method for a thermoelectric semiconductor, comprising: electrolytically etching a thermoelectric semiconductor in an electrolyte solution. 2. The method according to claim 1, wherein the electrolyte solution is a sodium hydroxide solution. 3. The method according to claim 2, wherein the concentration of the sodium hydroxide solution is 10 to 100 g /
1, a pretreatment method for plating a thermoelectric semiconductor. 4. The method according to claim 1, wherein the electrolytic etching is a periodic reverse electrolytic etching or an anodic electrolytic etching. 5. The pretreatment method according to claim 1, wherein the thermoelectric semiconductor is subjected to an acid treatment after the electrolytic etching in the electrolyte solution. 6. The method according to claim 5, wherein the acid activation treatment is a mixed solution of sulfuric acid having a concentration of 400 to 500 ml / l and an aqueous solution of hydrogen peroxide having a concentration of 10 to 50 ml / l. A pretreatment method for plating a thermoelectric semiconductor, which is performed for about 2 minutes.