JP2022153704A - Method of manufacturing substrate for power semiconductor and heat-resistant glass substrate - Google Patents

Abstract

To provide a substrate for power semiconductor and a heat-resistant substrate at low costs with superior manufacturing efficiency.SOLUTION: There is provided a method of manufacturing a substrate 11 for power semiconductor that includes in order: a contact layer forming process (step S1) of coating a glass substrate 10 by screen printing with contacting paste for securing adhesion between the glass substrate and an electrode; an electrode pattern layer forming process (step S2) of applying by screen printing metal particulate paste along a pattern forming the electrode; a wet layer forming process (step S3) of applying by screen printing paste for soldering for securing wettability in soldering a power semiconductor element to other components; and a solidifying process (step S4) of solidify respective paste parts by burning at predetermined temperature.SELECTED DRAWING: Figure 1

Description

The present invention relates to a technology for manufacturing substrates suitable for power semiconductors that control and supply electric power.

In recent years, the demand for so-called power semiconductors for high power and high voltage is increasing, such as the spread of electric vehicles. Since power semiconductors inevitably tend to reach high temperatures, heat resistance is required for substrates on which they are mounted. For this reason, ceramic substrates such as alumina substrates are used as substrates for power semiconductors.
Photolithography is used to form the electrodes on the substrate. That is, a metal layer is formed on the ceramic substrate (vacuum film formation) → resist layer formation → pattern exposure → development → etching → removal of the resist portion, and then mounting such as soldering of the power semiconductor is performed in the post-process. A ceramic substrate is manufactured.

However, the conventional technique has the following problems.
Conventional substrates for mounting power semiconductors have the problem that ceramics themselves are not inexpensive.
In addition, it is necessary to go through multiple processes such as vacuum deposition and photolithography.In addition, ceramics require high-temperature firing, and the hardness increases after firing, which generally causes chipping and cracking. Therefore, there is a problem that the separation after photolithography is difficult, and overall the manufacturing efficiency is not high.
Furthermore, there is also a method of forming a copper thick film circuit with a copper-based conductive paste on ceramics, but it is necessary to adjust the amount of the glass component in order to improve the adhesion, and if the amount of the glass component is small, the adhesion is poor. If the amount of the glass component is large, the adhesion is improved, but the electrical conductivity is deteriorated. In addition, the glass component is deposited on the surface of the conductor wiring by the baking treatment, resulting in poor solder wettability. There was also a problem that compounding was difficult.

JP 2008-7399 Japanese Patent Laid-Open No. 5-206635 Japanese Patent Laid-Open No. 8-298359 JP 2008-243840

SUMMARY OF THE INVENTION It is an object of the present invention to provide a substrate for a power semiconductor or a heat-resistant substrate that is excellent in manufacturing efficiency and inexpensive.

The method for manufacturing a power semiconductor substrate according to claim 1 includes an adhesion layer forming step of applying an adhesion paste for ensuring adhesion between the glass substrate and the electrode by screen printing to the glass substrate; An electrode pattern layer forming step of applying metal fine particle paste along the pattern to be formed by screen printing, and a soldering paste for ensuring wettability when soldering power semiconductor elements and other parts is applied by screen printing. It is characterized by sequentially including a wet layer forming step and a solidifying step of firing at a predetermined temperature to solidify each paste portion.

That is, the invention according to claim 1 increases the degree of freedom in material selection and preparation of metal fine particles and each binder by using different pastes, and improves the reliability and workability of soldering to the electrode and the adhesion of the electrode to the substrate. It is possible to manufacture an electrode substrate that secures both properties, has excellent heat resistance and is suitable for large current applications, using glass, which is cheaper than ceramics and has excellent workability, by a simple and inexpensive method.

Although the glass substrate is not particularly limited, it is preferable to use a glass substrate that does not deteriorate even in a high temperature environment and has a small expansion coefficient. Moreover, as will be described later, the substrate may be cut or indexed, so it is preferable that the substrate is suitable for such workability. Good quality and inexpensive silicate glass or borosilicate glass can be used. For example, liquid crystal display glass or the like can also be used.
Materials for ensuring adhesion in the adhesion paste may be appropriately selected and prepared according to the glass and metal fine particles (binder in some cases) to be used. For example, phenol resin can be used as a binder, and butyl carbitol can be used as a solvent.
The metal fine particle paste may also be appropriately selected and prepared by combining materials such as glass, adhesion paste, solder paste, and the like. Since the substrate is for a power semiconductor, the fine metal particles, that is, the filler, are preferably fine particles mainly composed of copper or silver. The particle size and particle size distribution may be appropriately designed, but the particle size is preferably on the order of micrometers to nanometers. A phenol resin can be used as the binder, and butyl carbitol and the like can be used as the solvent. The paste may contain a small amount of a dispersant or the like, as appropriate, as long as it does not affect the product using the substrate.
In the solder paste, the material for improving the wettability of the solder may also be appropriately selected and prepared according to the metal fine particle paste to be used. For example, a paste using silver-coated copper as a filler and an epoxy resin as a binder can be used.

Screen printing is a technique in which a paste is rubbed onto a plate (screen mask) directly above a substrate or directly above a lower layer, and a paste layer is transferred, applied, and formed through the mesh of the screen mask. Where the mesh (holes) is provided forms the pattern. In addition, since it is possible to apply multiple layers of coating easily, it is also possible to increase the thickness of the electrode as desired to reduce the resistance of the electrode and suppress heat generation.
Also, the screen mask is replaced according to the paste. The mesh portion of the screen mask used in the adhesive layer forming step and the screen mask used in the electrode pattern layer forming step have substantially the same shape (the same pattern) (the mesh portion for the adhesive layer may be slightly larger). In addition, if the screen mask used in the wet layer forming step has only the portion or region to be soldered to the power semiconductor element or other parts as the mesh portion, waste of the paste can be eliminated.
Screen printing for forming an insulating layer, an oxidation-resistant layer, and a protective layer may be added after the wet layer forming step, depending on the specification.
Solidification is defined in a broad sense, and includes the removal of each binder and solvent, and firing until fine metal particles combine to exhibit a desired resistance value. Drying and curing are also included.
In addition, in the present invention, the electrodes can be appropriately expressed as a circuit.

The method for manufacturing a power semiconductor substrate according to claim 2 is characterized in that, in the method for manufacturing a power semiconductor substrate according to claim 1, the electrode pattern layer forming step is repeated a plurality of times to increase the thickness of the electrode. do.

In other words, according to the second aspect of the present invention, it is possible to easily reduce the resistance of the electrode and suitably manufacture the power semiconductor substrate.

The heat-resistant glass substrate according to claim 3 is obtained by applying an adhesion paste to the glass substrate by screen printing to ensure adhesion between the glass substrate and the electrodes, and then applying a metal paste along the pattern for forming the electrodes. Fine particle paste is applied by screen printing, then soldering paste for ensuring wettability when soldering power semiconductor elements and other parts is applied by screen printing, and then baked at a predetermined temperature. The binder in the paste is dispersed to form a layer that secures solder wettability on part or all of the surface of the electrode pattern that is in close contact with the glass.

That is, the invention according to claim 3 ensures both the reliability and workability of soldering to the electrode and the adhesion of the electrode to the substrate due to the high degree of design freedom, heat resistance and workability. It is possible to provide an inexpensive electrode substrate that is excellent in

Diffusion of the binder means diffusion of unnecessary components, and includes diffusion of solvents and the like.

When the electrode pattern layers are formed a plurality of times as in claim 2, depending on the viscosity and properties of the paste, a drying process for drying the previous electrode pattern layer may be interposed as appropriate to ensure stable lamination of each layer. You may do so.

Further, the three-dimensional circuit may be formed by including the electrode pattern layer forming step with different patterns a plurality of times and interposing the insulating layer forming step for forming the insulating layer when the pattern is switched. Thereby, the degree of freedom in designing the electrodes can be increased.
At this time, the insulating layer may be formed by screen-printing a paste mainly composed of fine particles of an insulating substance, or by inserting a separate (local) insulating sheet.

Also, a separation step of cutting or indexing the glass substrate may be further included. As a result, a large number of power semiconductor substrates having the same pattern or a plurality of patterns can be manufactured from a single glass substrate, and manufacturing efficiency can be improved. In addition, it is less likely to be damaged during processing compared to ceramics, improves the yield, and makes it possible to supply substrates at a low cost.
The separation process may be performed before or after soldering the power semiconductor element and other parts, and may be determined in consideration of the processes before and after and workability.

According to the present invention, a power semiconductor substrate or a heat-resistant substrate can be provided at low cost with excellent manufacturing efficiency.

4 is a flow chart showing a method of manufacturing a power semiconductor substrate according to Embodiment 1; It is a schematic diagram which showed the mode of layer formation. Among these, FIG. 2(a) is a plan view of the printed electrode pattern layer, FIG. 2(b) is a plan view of the wetting layer itself, and FIG. 2(c) is a plan view immediately after the wetting layer is formed. It is a top view of a board|substrate. 6 is a flow chart showing a method for manufacturing a heat-resistant substrate for power semiconductors according to Embodiment 2. FIG.

[Embodiment 1]
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a flow chart showing an embodiment of a method for manufacturing a power semiconductor substrate according to the present invention. Schematic diagrams showing how electrode patterns and the like are formed are added to the right side of the flow chart.

Since the screen printing machine or screen printing technique used in the present invention is a general-purpose one, detailed description of its configuration is omitted.

In this embodiment, the paste used has the following features.
・Adhesion paste: A paste with a high resin component ・Metal fine particle paste: A highly conductive paste that mainly uses copper fine particle powder with a particle size of 10 nm to 200 μm ・Solder paste: A paste that has a low resin component and is difficult to oxidize

Here, an example in which 4×5 glass substrates 10 of 200 mm×200 mm×4 mm are arranged and printed will be described. The size of the printing surface is 800 mm×1000 mm. The glass substrate 10 is made of commercially available borosilicate glass for liquid crystal televisions. Glass manufactured for liquid crystal televisions is mass-produced, is easily available, is inexpensive, and has no irregularity in plane (excellent flatness), and is suitable.

First, the adhesion layer 20 is formed on the surface of the glass substrate 10 (step S1).
The adhesion layer 20 is a layer interposed so that the electrode 35, which is essentially made of copper derived from the electrode pattern layer 30, is fully adhered to the glass substrate 10 and is not peeled off.
When forming the adhesion layer 20, first, a screen mask formed with a mesh having the same shape as the electrode 35 is fixed above the glass substrate 10 with a clearance of 0.5 mm. Next, an adhesion paste is placed on the screen mask, and the same paste is also applied to the squeegee. While pressing the squeegee against the screen mask with a predetermined pressure or sinking depth, the squeegee is moved from one end of the screen mask to the other at a predetermined speed.
By the above operation, the adhesion layer 20 is transferred and formed on the glass substrate 10 along the shape of the electrode.

In the subsequent formation of each layer, a drying step may be interposed according to the specification in order to improve the coating stability of the layer placed thereon. Note that the drying step does not necessarily mean heating, and it is sufficient if the surface properties are such that the paste can be stably adhered thereon, and an embodiment in which the substrate is left for a predetermined period of time is also included.

Next, the electrode pattern layer 30 is formed on the adhesion layer 20 (step S2a).
The electrode pattern layer 30 refers to a layer from which the binder is removed (that is, diffused) in the firing step (step S4) to become the electrode 35 made of copper.
When forming the electrode pattern layer 30, first, a screen mask having a mesh formed on the portion to be the electrode 35 is fixed above the adhesion layer 20 with a clearance of 0.5 mm plus the increase in film thickness. Next, a metal fine particle paste is placed on the screen mask, and the same paste is also applied to the squeegee. While pressing the squeegee against the screen mask with a predetermined pressure or sinking depth, the squeegee is moved from one end of the screen mask to the other at a predetermined speed.
Here, layer formation is performed multiple times based on the design value for the low resistance of the electrode 35 . In this embodiment, the thickness is three layers. That is, the electrode pattern layer 30 is placed again (step S2b), and the electrode pattern layer 30 is further placed (step S2c).
By the above operation, the electrode pattern layer 30 having the same shape as the adhesion layer 20 is formed on the adhesion layer 20 . The thickness of the electrode pattern layer 30 is 10 μm after one printing and 30 μm after three printings.
The clearance between the screen mask and the adhesion layer 20 at the time of printing may be fixed at a position that does not add the increase in film thickness because the film thickness formed by screen printing is 10 μm.

Next, a wetting layer 40 is formed on the electrode pattern layer 30 (step S3).
The wetting layer 40 is a layer placed to ensure wettability when soldering power semiconductor elements and other parts to be mounted in a later process.
When forming the wetting layer 40, first, a screen mask having a mesh formed only around the legs of the element is fixed above the electrode pattern layer 30 with a clearance of 0.5 mm plus an increase in film thickness. Next, paste for soldering is put on the screen mask, and the same paste is applied to the squeegee. While pressing the squeegee against the screen mask with a predetermined pressure or sinking depth, the squeegee is moved from one end of the screen mask to the other at a predetermined speed.
Through the above operation, the wetting layer 40 is partially formed on the electrode pattern layer 30 .

The mesh of the screen mask in each process has a thickness and hole size suitable for each paste.

Next, the glass substrate 10 formed with each layer is baked (step S4). The maximum temperature and baking time, and the temperature rising and cooling steps can be designed as appropriate.
As a result, the binder in each paste is blown off, and the electrode is fully adhered to the glass substrate 10. A low-resistance copper electrode in which good spot wettability is ensured in the soldered portion. 35 are formed. The substrate in this state is called substrate 11 .

Next, the power semiconductor element and other parts are soldered to the board 11 (step S5).
Finally, the substrate 11 is cut out and separated into products 13 to which power semiconductor elements and other parts are attached (step S6). For cutting out the substrate 11, a glass cutting technique may be appropriately used. A groove for cutting may be formed in the glass substrate 10 from the beginning.

Through the above steps, the product 13 on which the power semiconductor is mounted can be obtained. A power semiconductor substrate can be obtained by cutting the substrate 11 before placing the power semiconductor thereon.
In addition, the mode of layer formation is shown in FIG.

[Embodiment 2]
Next, a method for manufacturing a three-dimensionally crossed heat-resistant substrate for a power semiconductor will be described.
FIG. 3 is a flow chart for manufacturing a three-dimensionally crossed heat-resistant substrate for power semiconductors. An enlarged schematic diagram showing how the electrode patterns and the like are formed is added to the right side of the flow chart.

Note that description of steps similar to those of the first embodiment will be omitted as appropriate.
In addition to the paste of Embodiment 1, the following paste is also used in this embodiment.
・Insulating paste: Paste containing a large amount of insulating substances

First, the adhesion layer 20 is formed on the surface of the glass substrate 10 (step S1).
The adhesion layer 20 is a layer interposed so that the electrodes 35 and 36 are fully adhered to the glass substrate 10 and are not peeled off.

Next, the electrode pattern layer 30 is formed on the adhesion layer 20 (step S2a).
Furthermore, the electrode pattern layer 30 is placed thereon (step S2b).

Next, an insulating layer 50 is formed (step S3).
The insulating layer 50 is a layer interposed at the intersection of the patterned electrode layer 30 and the patterned electrode layer 31 placed directly above the insulating layer 50 . Provided to prevent short-circuiting of the electrodes.
When the insulating layer 50 is formed, a screen mask having meshes formed at the intersections of the electrodes is fixed above the electrode pattern layer 30 with a clearance of 0.5 mm plus an increase in film thickness. Next, an insulating paste is placed on the screen mask, and the same paste is also applied to the squeegee. While pressing the squeegee against the screen mask with a predetermined pressure or sinking depth, the squeegee is moved from one end of the screen mask to the other at a predetermined speed.
The insulating layer 50 is formed on the electrode pattern layer 30 by the above operation.

Next, an electrode pattern layer 31 is formed (step S4a).
Furthermore, the electrode pattern layer 31 is placed thereon (step S4b).
Like the electrode pattern layer 30, the electrode pattern layer 31 is a layer that will become the electrode 36 made of copper after the binder is removed in the baking step (step S6). It should be noted that the electrodes 35 and 36 have an intersection and are not the same.
When forming the electrode pattern layer 31, first, a screen mask having a mesh formed on the portion to be the electrode 36 is fixed above the insulating layer 50 with a clearance of 0.5 mm plus the thickness increase. Next, a metal fine particle paste is placed on the screen mask, and the same paste is also applied to the squeegee. While pressing the squeegee against the screen mask with a predetermined pressure or sinking depth, the squeegee is moved from one end of the screen mask to the other at a predetermined speed.
Here, layer formation is performed multiple times based on the design value for reducing the resistance of the electrode 36 . In this embodiment, the thickness is two layers.
The electrode 36 is formed over the adhesion layer 20 and the insulating layer 50 and has a height difference. This can be done by partially changing the holes and thickness of the mesh, and depending on the aspect of the specification, for example, in step S4a, the electrode pattern layer 31 is formed by separately using different screen masks and performing a plurality of separate paintings. Also, since the film thickness of the electrode 36 is 140 μm as will be described later, it is not necessary to deal with the height difference.
By the above operation, the electrode pattern layer 31 having three-dimensional intersections is formed.

Next, a wetting layer 40 is formed on the electrode pattern layer 31 (step S5).
Next, the glass substrate 10 formed with each layer is baked (step S6). The substrate in this state is called substrate 12 .

Finally, the substrate 12 is cut out (step S7). As a result, a heat-resistant substrate 14 that can be used in high-temperature environments such as for power semiconductors can be obtained.

As described above, according to the present invention, a glass substrate is used in place of a ceramic substrate which is poor in workability and requires vacuum deposition, so that electrodes can be easily formed at normal pressure. Excellent dimensional stability.
In addition, in order to use it for large currents, it is necessary to increase the ratio of metal fine particles in the paste in addition to thick coating, and there is a possibility that the adhesion to the glass will be impaired. A paste can be interposed, and adhesion reliability can be easily secured or improved.
Similarly, there is a possibility that the wettability of the solder may be impaired depending on the type, particle size, ratio, type of binder, etc. of the metal fine particles. It is possible to easily secure or improve the wettability of the solder.

It should be noted that the present invention is not limited to the above embodiments.
For example, the adhesive layer may be 20 μm thick, the electrode pattern layer may be 10 μm thick by one printing, 100 μm thick by ten printings, the wetting layer may be 20 μm thick, and the insulating layer may be 20 μm thick.
When the film thickness is important, the thickness may be 20 μm, and when fine lines are to be formed, the thickness may be 10 μm.

According to the present invention, a power semiconductor substrate or a heat-resistant substrate can be provided at low cost with excellent manufacturing efficiency.

10 Glass substrate 11 Substrate 12 Substrate 13 Product 14 Heat-resistant substrate 20 Adhesion layer 30 Electrode pattern layer 31 Electrode pattern layer 35 Electrode 36 Electrode 40 Wetting layer 50 Insulating layer

Claims (3)

an adhesion layer forming step of applying an adhesion paste for ensuring adhesion between the glass substrate and the electrode by screen printing;
an electrode pattern layer forming step of applying a metal fine particle paste by screen printing along a pattern for forming an electrode;
A wet layer forming step of applying solder paste by screen printing to ensure wettability when soldering power semiconductor elements and other parts;
A solidification step of firing at a predetermined temperature to solidify each paste portion;
A method for manufacturing a power semiconductor substrate, comprising: 2. The method of manufacturing a power semiconductor substrate according to claim 1, wherein the electrode pattern layer forming step is repeated a plurality of times to increase the thickness of the electrode. An adhesion paste is applied by screen printing to ensure the adhesion between the glass substrate and the electrodes,
Next, a metal fine particle paste is applied by screen printing along the pattern for forming the electrodes,
Next, a soldering paste for ensuring wettability when soldering the power semiconductor element and other parts is applied by screen printing,
After that, sintering at a predetermined temperature to dissipate the binder in each paste,
A heat-resistant glass substrate, wherein a layer ensuring solder wettability is formed on part or all of the surface of an electrode pattern in close contact with the glass.

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