JP2671603B2 - Flux-free soldering method - Google Patents

Description

Description: TECHNICAL FIELD The present invention is suitable for use in the case of joining a minute solder joint portion requiring a high degree of airtightness without using a flux, such as a pressure sensor unit. And fluxless soldering method.

BACKGROUND ART For example, a solder joint portion of a pressure sensor unit has a minute joint dimension of about 0.5 mm and requires a high degree of airtightness such as a leak amount of 1 × 10 ^-11 atm · cc / s or less. . Therefore, conventionally, in order to improve the solder wettability, flux is applied to the joint surface for soldering.

However, when heating is performed with a flux interposed, gas is generated from this flux and remains as a void in the soldered portion, and this void becomes the main cause of poor airtightness at the joint. Therefore, it becomes difficult to improve the airtightness of the joint, especially when the joint has a very small size. Also, it is necessary to wash the flux residue after soldering, which increases the number of soldering steps,
Since a CFC-based solvent is used as a cleaning agent, it is not preferable in terms of environmental protection.

For this reason, as a flux-free soldering method, there is a method for improving the solder wetting balance of the joint surfaces of the members to be joined arranged vertically by utilizing the effect of the solder flow-out due to the load and the self weight of the solder. It is proposed in Japanese Patent Publication No. However, according to this method, in a pressure sensor having a sensor chip in which a highly integrated semiconductor circuit is integrated, when the glass pedestal and the metal stem are joined, the sensor chip surface becomes the assembling direction in which the jig contacts. However, there is a problem in that minute scratches are attached to the surface of the sensor chip, resulting in defective electrical characteristics.

The present invention has been made in view of the above points, and even when a pressure sensor unit having a sensor chip containing a highly integrated semiconductor circuit is joined to a metal stem, An object of the present invention is to provide a flux-free soldering method capable of improving the solder wetting balance of both solder joint surfaces in a solder joint portion without causing scratches.

DISCLOSURE OF THE INVENTION Therefore, according to the present invention, when forming a nickel layer for solder joining and an oxidation preventing layer of the nickel layer on the surface of a member to be joined, the oxidation preventing layer is provided before the soldering. In relation to the heat history of the member, the nickel layer of the nickel layer is formed to a film thickness that prevents the nickel from being exposed on the outermost surface of the members to be joined after the heat history, and the solder is heated in a reducing atmosphere. The foil is melted and soldered to other members to be joined.

According to such a soldering method, even if the joined member is subjected to thermal history before soldering, the nickel of the underlying nickel layer is exposed to the outermost surface of the joined member because of the upper antioxidant layer. It can be effectively suppressed by the film thickness, and there is substantially no deterioration in solder wettability on the joint surface of the members to be joined.

Therefore, even if the load applied to the joint portion during solder joining is not increased, solder wetting is promoted, and the solder wetting on the facing surfaces is promoted to maintain the solder wetting balance on the joining surfaces of the members to be joined arranged above and below. In addition to the above-mentioned effect, good solder wetting of the joint surface of the members to be joined can be realized, and since the solder joint is heated in a reducing atmosphere, a highly airtight joint can be obtained without flux. Soldering is possible.

Therefore, it is not necessary to increase the load applied to the joint portion at the time of solder joining, and for example, even when a pressure sensor unit having a sensor chip containing a highly integrated semiconductor circuit is joined to a metal stem, It is not necessary to apply a load with a metal stem on the side, or to apply a load with another weight, and therefore, the problem of scratching the surface of the sensor chip can be eliminated.

In addition, by making the soldering flux-free,
The cleaning process of flux residue after soldering can be eliminated,
Not only will the assembly be automated, but it will also be effective for environmental protection such as CFC removal.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a configuration when a soldering method according to an embodiment of the present invention is applied to assembly of a pressure sensor unit, and FIGS. 2 and 3 are glass pedestals before and after heat history, respectively. Fig. 4 is a diagram showing the result of Auger analysis of the surface, Fig. 4 is a characteristic diagram showing the relationship between the gold (Au) film thickness on the glass pedestal surface and the detection intensity ratio of nickel (Ni) or oxygen (O), and Fig. 5 is the glass pedestal surface. of
FIG. 6 is a characteristic diagram showing the relationship between the Au film thickness and the solder wetted area, FIG. 6 is a characteristic diagram showing the relationship between the Au film thickness on the glass pedestal surface and the void area ratio of the soldered portion, and FIG. 7 is the load during soldering. FIG. 8 is a characteristic diagram showing a relationship with the airtight non-defective rate after soldering, and FIG. 8 is a characteristic diagram showing the relationship between the Au film thickness on the glass pedestal surface and the airtight non-defective rate after soldering.

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. This embodiment shows a case where a pressure sensor having a small joint portion size and a high airtightness at the joint portion is assembled, and FIG. 1 shows the configuration at the time of soldering.

The pressure sensor is, for example, a 42 alloy (Fe58%, N
It is assembled by joining to a metallic stem 3 made of i42%) or the like. Here, the stem 3 has a pressure introducing passage 6 formed in the central axis portion thereof, and the glass pedestal 1 has a pressure introducing port 5 reaching the sensor chip 4 formed in the central axis portion thereof. The introduction port 5 and the pressure introduction passage 6 are configured to be coaxially connected and connected. With this configuration, the measured pressure introduced into the pressure introducing passage 6 acts on the diaphragm surface of the sensor chip 4 and is subjected to signal processing by the semiconductor circuit integrated in the chip 4. It is what is detected.

Here, in the present embodiment, the joining surfaces of the stem 3 are sequentially
The glass pedestal 1 is made of Pyrex glass (manufactured by Corning Incorporated), which is Ni-plated or Ni-B-plated, and Ti, Ni, Au metal thin film layers are sequentially formed on the joint surface by vapor deposition. ing.

When joining the stem 3 and the glass pedestal 1 as described above, in the present embodiment, as shown in FIG. 1, the stem 3 is set with respect to the jig 7 with its solder joint surface facing upward. And
With the stem 3 set to the jig 7 in this manner, the solder foil 2 having a thickness of about 45 to 50 μm is placed on the joining region of the stem 3 and the glass pedestal 1 is mounted on the solder foil 2. The solder joint surface set on the end surface opposite to the chip 4 arrangement surface is placed as the lower side.

In this way, if the assembly structure of the stem 3 and the glass pedestal 1 is set by the jig 7, this is set as, for example, H ₂ / (H
₂ + N ₂ ) = 30% or more, preferably 30% to 50% In a reducing atmosphere, heated to 250 to 300 ° C., the solder foil 2 is melted and soldered together.

By the way, on the solder joint surface (lower side) of the glass pedestal 1, before the pressure introduction port 5 is arranged, as described above, a Ti layer for soldering the glass and the solder joint layer (Ni), and solder A metal thin film layer consisting of a Ni layer for joining the layers and an Au layer for preventing oxidation of the Ni layer is vapor-deposited. The glass pedestal 1 has the sensor chip 4 on the upper surface side after the pressure introduction port 5 is provided. Anodically bonded. Here, this anodic bonding is performed, for example, under the conditions of 360 ° C. for 15 minutes, and during this anodic bonding, the Ni layer and the Au layer undergo a thermal history, and the diffusion progresses in the Ni layer and the Au layer. .

2 and 3 are the Auger analysis results of the bonding surface of the glass pedestal 1 before soldering of the conventional structure.
Shows before anodic bonding, and FIG. 3 shows after anodic bonding. Further, each (A) figure shows the surface structure, and (B) figure shows the investigation result by the relationship between the analysis depth and the detection intensity.

As can be seen from FIGS. 2 and 3, no oxide film was detected on the surface of the glass pedestal 1 including the metal thin film layer before anodic bonding, whereas after anodic bonding, the cooling atmosphere after the bonding was reduced. Even in the atmosphere, an oxide film having a thickness of about 1 to 1.5 nm is growing. In the bonding surface of the glass pedestal 1, Ni diffuses and is exposed to the outermost surface due to the heat history during anodic bonding as described above, and the exposed Ni is oxidized by reacting with oxygen in the process after anodic bonding. However, if the oxide film is present, the solder wettability on the glass pedestal side is deteriorated, as pointed out in Japanese Patent Laid-Open No. 3-218950.

Even if the present inventors do not perform the solder bonding with the glass pedestal 1 inverted and the stem 3 on the upper side as in the conventional case,
That is, the film thickness of the Au layer formed on the bonding surface of the glass pedestal 1 was examined so that good solder bonding can be realized even in the assembling direction of FIG.

That is, the conventional Au layer was a simple antioxidation layer for the Ni layer, and since it was also a noble metal, it was formed with a thickness of about 80 nm, but in the present embodiment, it was formed with a thickness of 150 nm. I am trying to form.

Next, the function and effect of increasing the thickness of the Au layer will be described.

First, when the Auger image on the solder bonding surface side of the glass pedestal 1 after anodic bonding was observed, it was confirmed that Ni diffused / exposed to the outermost surface decreased as the Au film thickness increased. FIG. 4 shows the detection intensity ratio of Ni and O at this time, and it can be seen that the exposure of Ni decreases and the oxidation also decreases as the Au film thickness increases.

In addition, in FIG. 5, the bonding surface of the glass pedestal 1 is set up, the solder foil is placed on it, and the solder when heated in a reducing atmosphere of H ₂ / (H ₂ + N ₂ ) = 30% This shows the wetted area. From the figure, it can be seen that as the Au film thickness increases, the solder wettability becomes better, and the solder will wet the entire joint surface.

FIG. 6 shows the void area ratio of the soldered portion when the glass pedestal 1, the solder foil 2 and the stem 3 were assembled in the assembly direction shown in FIG. 1 and heated in a reducing atmosphere. It can be confirmed from FIG. 6 that the void area ratio decreases as the Au film thickness increases as the solder wettability of the glass pedestal 1 in FIG. 5 improves. Incidentally, the surface treatment of the stem 3 at this time is performed by Ni plating in order from the stem surface and Ni-B plating on the surface layer which is cheaper than Au. However, since the solder wettability of the glass pedestal 1 is improved, It was found that even if the load applied by the glass pedestal 1 and the sensor chip 4 was as small as 0.05 gf (load acting on the joint portion), the solder wettability of the facing Ni-B plating also tended to be improved.

FIG. 7 shows the relationship between the load during soldering and the good airtightness rate after soldering. The airtightness was determined by a leak test using a radioisotope, and the leak rate was 1 × 10 ^-11 atm.
・ Claims below cc / s were considered good. The surface treatment of the outermost surface of the stem 3 is Ni-B plating.

As in the present embodiment, the Au film thickness on the bonding surface of the glass pedestal 1 is set to 15
Assuming that it is 0 nm, the load is 0.05 gf / 0.08 as shown in FIG.
Even if it remains cm ² , it is 2.9gf / at 80nm Au film which is the conventional Au film thickness.
The same good result as when a load of 0.08 cm ² is applied is obtained. In addition, this load 2.9gf / 0.08cm ²
This corresponds to the load acting on the joint by setting the stem to the upper side in the inversion method disclosed in Japanese Patent Laid-Open No. 3-218950.

That is, in the present embodiment, the glass pedestal 1 arranged vertically with the glass pedestal side as the upper side is improved by improving the solder wettability of the glass pedestal surface without using the solder flushing effect due to the load of the stem or another weight. It is possible to improve the solder wetting balance on the joint surface of the stem 3 and the stem 3 and to perform good soldering. Even if the surface plating on the stem 3 side is made of inexpensive Ni-B plating, although the solder wets more slowly than Au, it improves the wettability due to the solder sacrificial weight and improves the solder wet balance of the joint surface, resulting in a uniform Good soldering can be achieved and good soldering is possible. Therefore, it is possible to realize a flux-free soldering method capable of assembling a pressure sensor with high airtightness and high bonding strength without damaging the surface of the sensor chip 4 having a highly integrated semiconductor circuit.

FIG. 8 shows the relationship between the Au film thickness of the glass pedestal 1 and the airtight non-defective rate required for the pressure sensor. The surface treatment of the outermost surface of the stem 3 is Ni-B plating, and the load is 0.
It is 05 gf / 0.08 cm ² .

In order to obtain better airtightness than in Fig. 8, the Au film thickness should be about 13
It turns out that it should be set to 0 nm. Further, when Au is contained in the solder in an amount of 4% by weight or more, the Au—Sn alloy is overgrown and causes strength deterioration, so that the upper limit of the thickness of the Au layer is considered to be about 360 nm. (This is due to the fact that in the above-mentioned one embodiment
Calculated as containing 4% by weight of Au). That is, although the case where the Au film thickness is formed to 150 nm is shown in the embodiment, the Au film thickness may be formed to approximately 130 nm to 360 nm.

Incidentally, as in the above example, the surface area of the component placed on the lower side during assembly is larger, and the solder wettability is slightly inferior (Ni-B / Ni plating), the area is small. It suffices to improve the solder wettability on the joint surface of the upper part. However, when the area of the lower part is large and the solder wettability is good (for example, Au plating), in order to prevent the solder shrinkage due to the excessive flow of solder, the solder wettability of the lower part is A means (for example, a weir, a groove or a partial plating treatment for stopping the flow of the solder) may be provided to limit only the joint portion of the above.

INDUSTRIAL APPLICABILITY As described above, the flux-free soldering method of the present invention is effectively applied to soldering when a joint having a minute joint surface and high airtightness and high joint strength is required. It is possible and can be effectively applied, for example, when assembling a pressure sensor.

Claims (16)

(57) [Claims] 1. When the surface of a member to be joined is composed of a nickel layer and an antioxidation layer of the nickel layer and is subjected to a heat history before the soldering step, after the heat history, the nickel in the nickel layer is A step of forming the anti-oxidation layer to a thickness that suppresses exposure to the outermost surface; a step of setting the member on the surface side thereof so as to face another member to be joined via a solder foil; A step of heating the members to be joined in a reducing atmosphere to melt the solder foil for soldering, and a fluxless soldering method. 2. The step of forming the anti-oxidation layer comprises depositing about 130 gold.
The method of fluxless soldering according to claim 1, characterized in that it is a step of forming a film in a thickness of up to 360 nm. 3. The joint surface of the member to be joined on which the antioxidation layer is formed is smaller than the joint surface of the other member to be joined, and the step of setting the other face in the direction of gravity of the other member to be joined. The fluxless soldering method according to claim 1, wherein the fluxless soldering method is set downward. 4. The joint surface of the member to be joined on which the antioxidation layer is formed is smaller than the joint surface of the other member to be joined, and the step of setting the other face to face the other member to be joined in the gravity direction. The fluxless soldering method according to claim 2, wherein the fluxless soldering method is set downward. 5. The solder wettability of the joint surface of the other joined member is inferior to the solder wettability of the joint surface of the joined member on which the antioxidant layer is formed after the thermal history. 5. The fluxless soldering method according to claim 4. 6. The fluxless soldering method according to claim 5, wherein the joint surface of the other member to be joined is plated with nickel-boron. 7. The fluxless soldering method according to claim 2, wherein the reducing atmosphere in the soldering step is a mixed gas atmosphere of hydrogen and nitrogen. 8. The hydrogen concentration in the mixed gas atmosphere is 30.
The fluxless soldering method according to claim 7, wherein the fluxless soldering method is about 10% or more. 9. Of the first and second members to be soldered,
Forming a nickel layer on the surface of the solder joint surface of at least one member and an oxidation preventing layer of this nickel layer, and applying a heat history; A second step of facing each other, and a third step of heating the first and second members in a reducing atmosphere to melt and solder the solder foil, and the first step is the heat treatment. A flux-free soldering method comprising the step of forming the antioxidation layer to a film thickness that suppresses the nickel of the nickel layer from being exposed on the outermost surface of the member after a history. 10. The step of forming the anti-oxidation layer comprises depositing about 13 gold.
10. The fluxless soldering method according to claim 9, which is a step of forming a film in a thickness of 0 to 360 nm. 11. The fluxless soldering method according to claim 10, wherein the reducing atmosphere in the soldering step is a mixed gas atmosphere of hydrogen and nitrogen. 12. A step of forming a nickel film on one surface of a glass member, further forming a gold film at about 130 to 360 nm, and further anodic bonding a silicon chip to the other surface of the glass member, A step of placing the glass member on the metal member via the solder foil with one surface thereof as the bonding surface, and heating the glass member and the metal member in a reducing atmosphere to melt the solder foil. And a flux-free soldering method, which comprises a step of soldering. 13. The fluxless soldering method according to claim 12, wherein the surface of the metal member has a larger area than one surface of the glass member. 14. The flux-free soldering method according to claim 13, wherein the surface of the metal member is inferior in solder wettability to one surface of the glass member. 15. The fluxless soldering method according to claim 14, wherein the surface of the metal member is plated with nickel-boron. 16. The fluxless soldering method according to claim 12, wherein the reducing atmosphere in the soldering step is a mixed gas atmosphere of hydrogen and nitrogen having a hydrogen concentration of about 30% or more. .