JP3605986B2 - Method for forming partial plating film of thermoelectric semiconductor - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for forming a partially plated film of a thermoelectric semiconductor.
[0002]
[Prior art]
A thermoelectric semiconductor device electrically connects a large number of p-type thermoelectric semiconductor chips and an n-type thermoelectric semiconductor chip, generates cold and hot heat by energizing, and uses the cold and / or heat for various purposes. Is what you do.
BACKGROUND ART A thermoelectric semiconductor chip, which is a main component of a thermoelectric semiconductor device, 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.
[0003]
For example, when connecting a thermoelectric semiconductor chip to an electrode made of copper or the like on a substrate by soldering, to prevent the tin component of the solder from diffusing into the thermoelectric semiconductor and deteriorating the quality performance. In order to ensure solder wettability, it is necessary to form a plating film for solder bonding.
In order to form such a plating film on a thermoelectric semiconductor, it is advantageous in terms of productivity and the like to employ electroless plating which can be formed only by immersion in a plating bath. In the case of using a plating bath, it is impossible to perform electroless plating on a thermoelectric semiconductor substrate composed of a bismuth-tellurium-based intermetallic compound or an antimony-tellurium-based intermetallic compound. It was necessary to deposit a plating film by electroless plating.
[0004]
Further, when the plating film is formed as the bonding plating film described above, since the formation of the plating film on the side surface of the chip needs to be avoided from the viewpoint of preventing leakage, both main surfaces of the thermoelectric semiconductor wafer are plated. Thereafter, the wafer is divided into thermoelectric semiconductor chips by dicing, thereby producing chips without depositing a plating film on the side surfaces of the thermoelectric semiconductor chips.
[0005]
[Problems to be solved by the invention]
However, in the conventional method of forming a plating film by performing the above-described two-stage plating, power must be supplied to the thermoelectric semiconductor in the first electrolytic plating step. The plating film becomes thinner, and hence the electroless plating film becomes thinner. As a result, the thickness of the plating film of each chip varies. If the plating film is thin, there arises a problem that tin components of the solder diffuse into the thermoelectric semiconductor, and if the plating film is thick, the production takes a long time, and the productivity is reduced. In addition, since the two-stage plating process is performed, the production process becomes longer, the productivity is reduced, and it is difficult to reduce the cost.
[0006]
The present invention has been made in view of the above problems, and, while reducing the variation in the thickness of the plating film, to realize a method for forming a partial plating film of a thermoelectric semiconductor capable of significantly improving the productivity. The primary purpose is.
Next, in the conventional method of dicing a wafer on which a plating film is plated as described above, peeling or scratching of the plating film always occurs at the corners of the chip, that is, at the edges of the main surface during dicing, and the tin of the solder is removed. There is a problem that the component diffuses from this portion into the thermoelectric semiconductor and deteriorates its characteristics. Of course, it is also conceivable to plate the plating film after dicing the wafer into chips and divide it into chips.In this case, it is necessary to supply power for electrolytic plating to each chip, and it is necessary to supply power to the side of each chip. In order to prevent the formation of the electrolytic plating layer, it is necessary to significantly extend the process, for example, it is necessary to cover the side surfaces with an electric insulating material.
In order to prevent the diffusion of the tin component of the solder at the edge (corner) of the chip, it is conceivable to solder only to the center of the plating film. However, such a method increases the electric resistance of the device. Or poor connection is not preferred.
[0007]
SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is possible to form a plating film (plating film for solder) satisfactorily over the entire main surface of a thermoelectric semiconductor to be plated, and particularly to plating for solder at an edge portion thereof. It is a second object of the present invention to realize a method for forming a partially plated film of a thermoelectric semiconductor in which scratches and peeling of the film are prevented and the diffusion of tin components of the solder into the thermoelectric semiconductor is improved.
[0008]
[Means for Solving the Problems]
According to the method of claim 1, by irradiating the thermoelectric semiconductor immersed in the electroless plating bath with a laser beam, an electroplating film is not formed on the thermoelectric semiconductor in advance, but directly by the electroless plating step only. A partial plating film is formed. The present invention has the following operational effects as compared with the conventional manufacturing method which requires a two-stage plating process including electrolytic plating and electroless plating.
First, since the present invention does not require an electrolytic plating step, it is possible to prevent spatial variation in the thickness of the solder plating film due to the resistance voltage drop of the thermoelectric semiconductor substrate, and to improve productivity. Things.
[0009]
Conventionally, it is possible to form an electroless plating film on a special metal surface or an insulating material surface, but it is not known to directly form an electroless plating film on a thermoelectric semiconductor. In order to form an electroless plating film, it was necessary to apply and form an electroplating film beforehand.
As a result of various experiments, the present inventors have found that an electroless plating film can be formed on a thermoelectric semiconductor surface without previously applying an electrolytic plating film by laser light irradiation.
[0010]
According to the present invention, the thermoelectric semiconductor chip having the final main surface shape is formed in advance by dividing the wafer or the rod into the final shape, and the thermoelectric semiconductor chip is immersed in an electroless plating bath and irradiated with laser. By doing so, a plating film is formed.
The present invention has the following advantages as compared with the conventional manufacturing method in which a thermoelectric semiconductor chip is formed by dividing a wafer on which a solder plating film is plated.
[0011]
First, according to the present invention, after the thermoelectric semiconductor chip is formed into the final shape, the plating film is subjected to electroless plating using laser light, so that the plating film for solder can be formed by a simple production process.
After dividing the wafer into chips, compared to the conventional method of plating the plating film in a two-stage plating process, a step of supplying power to each chip for electrolytic plating, There is an effect that all steps related to electrolytic plating can be omitted, such as a step of coating the side surface with a wax (electric insulating film) and peeling it off after plating.
[0012]
According to the method of the second aspect , the thermoelectric semiconductor is immersed in the electroless plating bath while irradiating the pair of main surfaces with a laser beam, thereby forming an electrolytic plating film on the main surface of the thermoelectric semiconductor substrate in advance. Without electroless plating, a highly conductive solder plating film that can prevent, for example, tin diffusion can be produced directly.
This eliminates the necessity of attaching and detaching the side surface insulating protective film required for electrolytic plating, so that the production process can be remarkably shortened, and the cost and yield of forming a plated film for solder can be improved. In other words, when electrolytic plating is performed on this chip, the electric insulating film on the side surface of the chip inevitably adheres not only to the side surface of the chip but also to the edge of the main surface. However, according to the present invention, it is difficult to solve the problem that it is difficult to form a plating film, and it is difficult to prevent the diffusion of the tin component of the solder through the edge. The problem can be solved by a very simple process of irradiation.
[0013]
In addition, since the main surface of the thermoelectric semiconductor chip can be prevented from being scratched or peeled off particularly at the edge of the thermoelectric semiconductor chip, when the main surface of the thermoelectric semiconductor is soldered through this plating film, the tin component of the solder is reduced. It is possible to prevent the plating film from being diffused into the thermoelectric semiconductor chip through the damaged or peeled portions.
Furthermore, according to the present invention, as described above, since the plating film is not formed on the side surface of the chip not irradiated with the laser beam, the plating film is formed only on the main surface without insulatingly coating the side surface of the chip divided into the final shape. Since the chip can be formed, the chip can be formed by cutting a bar or the like without using a wafer, and the effect of facilitating the production of the thermoelectric semiconductor chip can be obtained. The tin component of the rod solder of the thermoelectric semiconductor and the thermoelectric semiconductor powder can be manufactured by a simple process of extruding while sintering by pressing while heating.
[0014]
In a preferred embodiment, the plating film is formed on the entire main surface of the thermoelectric semiconductor chip. By doing so, it is possible to favorably prevent the tin component of the solder from diffusing into the thermoelectric semiconductor chip, and to reduce the electric resistance loss.
According to the method of claim 3 , the thermoelectric semiconductor substrate is made of a bismuth-tellurium-based thermoelectric semiconductor material or an antimony-tellurium-based thermoelectric semiconductor material, and the electroless plating bath is a self-catalytic electroless plating bath. As a self-catalytic electroless plating bath, those having a usual composition can be employed. By doing so, it was found that a plated film having all of the tin diffusion preventing property, the solder wettability, and the good conductivity can be obtained.
[0015]
As described above, conventionally, formation of an electroless plating film on a thermoelectric semiconductor is not known, and in order to form an electroless plating film on the surface of a thermoelectric semiconductor, an electroplating film is applied in advance before the electroless plating film is formed. Needed to be formed.
On the other hand, the present inventors have conducted various experiments and found that, even if an electrolytic plating film was not previously applied, a bismuth-tellurium-based thermoelectric semiconductor material or an antimony-tellurium-based thermoelectric semiconductor material could be electrolessly plated by laser light irradiation. It has been found that a film can be formed directly.
[0016]
More specifically, conventionally, it is possible to perform self-catalytic electroless plating (using a redox reaction) on a Group VIII metal material, and to perform Fe, Cu, Ag by performing electrolytic plating in advance. , Au, Be, Ge, Al, C, V, Mo, Cr, Se, Ti, U, it is known that electroless plating can be performed, but Bi, Cd, Sb, Sn, Pb, Zn , As, and W are known to be capable of electroless plating unless their surfaces are well coated with a dissimilar metal (usually Ni). This is because these metals are catalyst poisons for the electroless plating reaction.
[0017]
The present inventors have found that, as described above, even with a thermoelectric semiconductor material containing Bi and Sb, electroless plating can be performed by irradiating a laser beam. This is probably due to the presence of tellurium and the reaction promoting effect by laser light.
According to the method of claim 4 , the electroless plating bath contains a nickel salt, sodium hypophosphite and a pH adjuster, and the plating film for solder is made of a Ni-P alloy. In this way, in addition to having tin diffusion preventing properties, solder wettability, and good conductivity, it is possible to obtain a strong plating film including P, so that the tin component of the solder diffuses into the thermoelectric semiconductor due to damage to the plating film. More effective for prevention.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Preferred embodiments of the present invention will be described below.
As the thermoelectric semiconductor, generally used, for example, a bismuth-tellurium-based thermoelectric semiconductor material or an antimony-tellurium-based thermoelectric semiconductor material can be used. In addition, a lead-germanium-based or silicon-germanium-based thermoelectric semiconductor material can be used. The thermoelectric semiconductor may be a single crystal, a polycrystal, or a sintered body.
[0019]
The plating film is preferably a metal or alloy having Sn barrier properties, and excellent in solder wettability and electrical conductivity. Ni-P alloys usually obtained using an autocatalytic electroless plating bath meet this requirement.
The laser beam heats the main surface of the thermoelectric semiconductor and the electroless plating bath in contact with the main surface, and improves the reactivity thereof. Therefore, various wavelengths can be used for the wavelength of the laser beam, but a near-infrared laser device that easily obtains a large output is particularly preferable. Similarly, the laser beam can be used in either pulse output or continuous output, but the former is more preferable. It is necessary that the laser beam is irradiated perpendicularly to the main surface of the thermoelectric semiconductor. This is important in that laser light is not irradiated on the side surface of the thermoelectric semiconductor.
[0020]
As the composition of the Ni—P electroless plating bath of the present invention, the same composition as that of a conventional electroless plating bath that does not emit laser light can be used. However, if the ambient temperature, that is, the temperature of the electroless plating bath or the thermoelectric semiconductor is too high, there is a possibility that a plating metal is deposited on the side surface of the uncovered thermoelectric semiconductor, so the electroless plating bath temperature is 100 ° C. or lower, preferably It is preferable to maintain the temperature at about room temperature.
[0021]
【Example】
A preferred embodiment of the present invention will be described with reference to the system diagram shown in FIG.
1 is a plating tank, 2 is a circulation pump, 3 is an adjustment tank, 4 is a YAG laser device, and 5 is a condenser lens device.
The circulating pump 2 allows the electroless plating solution to flow into the inside of the plating tank 1 from one side end face, flow out from the other side end face, and is adjusted to a predetermined composition by the adjustment tank 3 and circulated. The composition of the electroless plating bath is as follows.
Nickel sulfate 22.5g / L
Sodium hypophosphite 23.85 g / L
Lactic acid 27g / L
Sodium succinate 16g / L
pH 4.8
Temperature 20-70 ° C
A receiving table 11 is placed in the plating tank 1, and a large number of thermoelectric semiconductor chips 6 are mounted on a flat upper surface of the receiving table 11. The upper surface of the thermoelectric semiconductor chip 6 forms the main surface to be plated. A glass plate 12 is horizontally fixed to an upper surface of the plating tank 1, and a depth of a plating bath passage between a lower surface of the glass plate 12 and an upper surface of the receiving table 11 is set to be about mm. In addition, an XY turntable that two-dimensionally moves the plating tank 1 in the horizontal direction, a flow rate control device that maintains a constant flow rate of the plating bath, a pedestal elevating device that adjusts the depth of the plating bath passage, and a plating bath A radiator or cooler for adjusting the temperature is provided.
[0022]
The YAG laser device 4 has a maximum output of 400 W, an average output of 40 W, a pulse frequency of 100 Hz, a spot of 2 × 2 mm, and an irradiation interval of 5 to 30 seconds. The condenser lens device 5 can be moved up and down so that a spot of 2 × 2 mm can be formed on the upper surface of the chip.
Using the manufacturing apparatus described above, a 1 mm square chip made of a bismuth-tellurium-based sintered body was used as the thermoelectric semiconductor chip 6, and laser beam spot irradiation electroless plating was performed. The results are shown in chip cross-section photograph 1 (400 times). From the photograph, it was found that a Ni—P alloy film composed of a uniform film having a thickness of 2 to 3 μm was obtained.
[0023]
According to the experiment, if the peak output of the irradiated laser beam is too large, cracks may occur in the formed Ni—P alloy film or the thermoelectric semiconductor may be dissolved. The recommended energy density of the laser beam is preferably 1.25 to 5 W per square mm. If it is less than 1.25 W per square mm, a decrease in the film production speed becomes a problem, and if it exceeds 5 W per square mm, cracks in the formed film increase. It should be noted that some cracks having a small width do not hinder the prevention of Sn diffusion.
[0024]
Except that the tip was made of an antimony-tellurium-based sintered body, the same manufacturing process as above was performed. As a result, the same Ni-P alloy film as described above was obtained.
[Brief description of the drawings]
FIG. 1 is a system diagram showing a state of a manufacturing apparatus.
FIG. 2 is a cross-sectional photograph (× 400) of the obtained Ni—P alloy film.

Claims (4)

A method for forming a partially plated film of a thermoelectric semiconductor, wherein a partially plated film is formed on an irradiated portion of the thermoelectric semiconductor by irradiating a laser beam while immersing the thermoelectric semiconductor in an electroless plating bath,
The thermoelectric semiconductor is formed of a chip formed by dividing a wafer or a rod into a final shape, and the chip is irradiated with laser light while being immersed in an electroless plating bath to selectively form a plating film. A method for forming a partially plated film of a thermoelectric semiconductor, characterized by comprising: 2. The method according to claim 1 , wherein the thermoelectric semiconductor has a pair of main surfaces, and the main surface is irradiated with a laser beam to form a plating film for solder bonding. 3. The method according to claim 1 , wherein the thermoelectric semiconductor includes bismuth, tellurium, antimony, or tellurium. The thermoelectric semiconductor part according to any one of claims 1 to 3 , wherein the electroless plating bath contains a nickel salt, sodium hypophosphite and a pH adjuster, and the plating film is made of a Ni-P alloy. Plating film formation method.

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