JPH0416038B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a heat dissipating electrically insulating substrate for printed circuits that has excellent heat dissipating properties and electrically insulating properties.

[Prior Art] As one type of heat dissipating electrical insulating substrate for printed circuits based on a metal plate, one in which a metal foil such as copper foil is bonded to a metal plate such as aluminum or iron is known. In this case, in order to maintain electrical insulation between the metal plate and metal foil, glass cloth, kraft paper, etc. are impregnated with thermosetting resin such as epoxy resin.
Efforts have been made to insert an insulating material such as a prepreg that has been heat-treated to a semi-hardened (B-stage) state between the two, or to provide an insulating layer by oxidizing the surface of the metal plate.

However, the oxidation treatment of the metal surface has drawbacks such as the tendency for cracks to form in the metal oxide, which is the insulating layer, during external shaping. On the other hand, in a structure in which an insulating material such as prepreg is inserted, the thickness and uniformity of the insulating layer are determined by the glass cloth, kraft paper, etc. used as the aggregate, so it is easy to maintain electrical insulation and it is possible to Although it has the advantage that the thickness and uniformity of the insulating layer can be maintained relatively easily even when heated and pressurized, the use of glass cloth etc. increases the thickness of the insulating layer and greatly reduces the thermal conductivity. There is a problem that the heat dissipation properties of the substrate are poor.

The key to manufacturing a heat-dissipating electrically insulating board with excellent heat dissipation and electrical insulation is how to make the insulating layer between the metal plate and the metal foil as thin as possible while maintaining electrical insulation. One possible solution to this problem is to maintain electrical insulation with only an adhesive layer as thin as possible, for example several tens of micrometers, without using prepreg. With methods such as heating, pressing at a specified pressure all at once and holding for a specified period of time, etc.), the adhesive melts during heating and pressing, so slight fluctuations in pressing conditions such as the parallelism of the upper and lower hot platen surfaces of the pressure molding machine may occur. etc., it is often difficult to maintain electrical insulation due to variations in the thickness of the adhesive layer.
Furthermore, since the adhesive flows out at the ends of the insulating layer, the thickness becomes non-uniform, especially at these parts, resulting in a problem of poor product yield.

[Means for Solving the Problems] In order to solve the above problems, the inventors of the present invention have specifically studied the novel idea of ``maintaining electrical insulation with only the thinnest adhesive layer possible without using prepreg.'' As a result, we discovered that by controlling the heating and pressing method of the adhesive layer under specific conditions, it was possible to stably form a uniform and sufficiently thin insulating layer (adhesive layer) over the entire surface of the substrate for the first time. Ta.

Therefore, an object of the present invention is to produce a heat-dissipating electrically insulating substrate that stably forms a uniform and sufficiently thin insulating layer over the entire surface of the substrate using only an adhesive layer without using prepreg, and has excellent heat dissipating properties and electrical insulation properties. The purpose is to provide a method.

[Structure of the Invention] That is, the present invention includes: (1) A heat-dissipating electrical insulating substrate is manufactured by stacking and heat-treating multiple pairs of metal plates stacked on a metal foil coated with an epoxy resin adhesive uniformly. In the method, (a) the first step is to uniformly apply an epoxy resin adhesive to the metal foil in advance and then heat treat it to bring it to a B-stage state; (b) the temperature is at least 5°C above the softening point of the adhesive. Pressure is applied for a short time under low temperature conditions, and the above B-
A second step of physically adhering the adhesive layer in the stage state to the metal plate without softening and deforming it; (c) increasing the temperature without applying pressure to the extent that the adhesive layer maintains its initial thickness without deforming; A third layer that hardens to a maximum temperature and promotes adhesion with the metal plate.
Step (d) When the temperature range between the end point of gelation of the adhesive and the temperature range 30°C higher than the end point of gelation is reached, pressure treatment is performed again, and then pressure is applied at a constant temperature to remove the adhesive layer. A method for manufacturing a heat dissipating electrical insulating board, comprising: a fourth step of completely curing the adhesive layer while preventing deformation and adhering it to a metal plate.

(2) In the second step of the preceding paragraph (b), when performing the pressure treatment, the pressure is 30 to 50 kgf/cm ² (G) at room temperature or at a temperature at least 5°C lower than the softening point of the adhesive.
1 above, which is subjected to pressure treatment for 10 to 30 seconds under a pressure of
A method for manufacturing a heat dissipating electrically insulating substrate as described in 1.

(3) The above (1) or (2) uses any one of copper foil, aluminum foil, or nickel foil as the metal foil, and any one of aluminum plate, iron plate, aluminum alloy plate, or iron-based alloy plate as the metal plate. ) The method for manufacturing a heat-dissipating electrically insulating substrate.

(4) Gel time of epoxy resin at 160℃ is 10 to 30
The method for manufacturing a heat-dissipating electrically insulating substrate according to any one of (1) to (3) above, wherein

Our goal is to provide the following.

[Specific Description of the Invention] Next, the present invention will be described in detail in order to facilitate understanding of the present invention.

First, the epoxy resin adhesive is a known epoxy resin such as bisphenol A type mixed with a curing agent. Softening point 50~80℃, hardening point 110
-150°C, and those having a glass transition point of 130-150°C are preferred.

The metal foil used is copper foil, nickel foil, or aluminum foil with a thickness of about 10 to 50 μm. These foils are manufactured by electrolysis or rolling.

Apply a thickness of 20 to 40 μm (±2 μm) on one side of the metal foil in advance.
m) Apply a thick layer of epoxy resin adhesive evenly. After coating, it is subjected to a known heat treatment (for example, hot air drying treatment) at 80 to 150°C to bring it into a B-stage (semi-cured) state, thereby producing an adhesive-coated metal foil. This is the first aspect of the present invention.
At this stage, the adhesive layer remains uniform and sufficiently thin.

At this time, the adhesive has a gelation time of 160℃.
It is best to control the heat treatment so that the heating time is 10 to 30 seconds, preferably 15 to 25 seconds. If the gelation time is 40 seconds or more, the thickness of the insulating layer (adhesive layer) will vary greatly.

On the other hand, the metal plate is typically made of aluminum, iron, aluminum-based alloy, or iron-based alloy, has a thickness of 1 to 2 mm, and has the same dimensions as the metal foil, approximately 20 to 100 cm square. . After degreasing with trichlene or the like, it is preferable to roughen the surface by chemical conversion treatment or the like.

A plurality of pairs (3 to 6 pairs) of stacked metal plates are stacked on the adhesive-applied surface of the adhesive-coated metal foil, and heat and pressure treatments in the second to fourth steps are performed. In the present invention, the heating and pressurizing conditions in this step are particularly important.

FIG. 1 shows an example of the heating and pressing profile of the second to fourth steps of the present invention. A cushion material and a mirror plate are placed between the upper and lower heated platen surfaces of the pressure molding machine, and the plurality of pairs of metal foils and metal plates are placed through these, and the temperature is raised from room temperature. At a temperature _{T 1} that is at least 5°C lower than ^the softening point of (meaning) done under pressure. This is the second step of the present invention,
By applying pressure under the above conditions, the uniform and sufficiently thin B-stage adhesive layer obtained in the first step can be physically adhered to the metal plate without being softened and deformed. If pressure is applied above the above temperature, the adhesion with the metal plate will increase, but the adhesive layer will be softened and deformed, loss of uniformity, and variations in the thickness of the product will occur.

Thereafter, the forced pressurization is stopped, and the temperature is continued to rise without pressurizing. This is the third step of the present invention, whereby the uniform and sufficiently thin adhesive layer in the B-stage state is gradually cured to the extent that it does not deform while maintaining its initial thickness (up to approximately 80%). At the same time, adhesion with the metal plate is promoted. In addition,
If this step is carried out under pressure, the adhesive layer will be softened and deformed, resulting in loss of uniformity.

And the end point of adhesive gelation (denoted as T(g))
When the temperature range T ₂ , which is 30° C. higher than the end point of gelation, is reached, pressurization P ₂ is performed again at a pressure of 35 to 50 Kgf/cm ² , and then pressurization is performed at T ₃ at a constant temperature. In this case, under a constant temperature means a temperature range from the end point of gelation to a temperature range 30°C higher than the end point of gelation, but after applying pressure P ₂ again at temperature T ₂ , pressurization is performed at the same temperature. However, the higher the temperature, the shorter the curing time, so it is preferable to raise the temperature to a temperature as close as possible to a temperature 30°C higher than the end point of gelation (expressed as T (g + 30). ) is not preferable because the degree of crosslinking of the adhesive (layer) tends to be non-uniform and properties such as adhesive strength tend to decrease.

This is the fourth step of the present invention, and by applying pressure under the above conditions, it is possible to prevent the adhesive layer from deforming and sufficiently cure it, as well as to provide the necessary adhesive strength between the adhesive layer and the metal plate. . In addition, the third
Because the curing process is approximately 80%,
The deformation of the adhesive layer due to pressure in this step is slight.

An example of specific heating and pressurizing conditions for the second to fourth steps described above is as follows.

For example, when using an adhesive with a softening point of 60℃ and a gelation end point of 150℃, when the temperature reaches room temperature to 55℃ (e.g. 40℃), pressurize for about 20 seconds (second step), then Raise the temperature without applying pressure (third step), and when the temperature reaches 150-180°C (e.g. 160°C), apply pressure again and then hold at the curing temperature (e.g. 175°C) (fourth step) ,It turns out that.

As explained above, by controlling each heating and pressing method in the first to fourth steps of the present invention under specific conditions, for the first time, the thickness can be increased by using only the adhesive layer without using prepreg. A thin insulating layer (adhesive layer) of several tens of micrometers can be formed uniformly and accurately over the entire surface. As a result, there is almost no variation in layer thickness between products, and since the thickness is uniform all the way to the edge of the substrate, the product yield is greatly improved.

The effects will be explained below based on examples.

Example 1 After applying epoxy adhesive to a 35 μm thick electrolytic copper foil (250 mm x 250 mm) with a thickness accuracy of 40 ± 2 μm, it was dried with hot air at 100°C to bring it to a B-stage state, and the adhesive was attached. A metal foil was prepared (first step).
Note that the gelation time (@160°C) of the adhesive is 20 seconds. An aluminum plate (250 mm x 250 mm) with a thickness of 1.0 mm was used as the metal plate, and three cushion materials were placed between the upper and lower heating plates of the pressure forming machine, and between these, the adhesive-coated metal foil and the metal Five pairs of overlapping plates were placed one on top of the other, and heat and pressure treatment was performed under the following conditions.

Heat and pressure treatment conditions; Second step: Pressure at room temperature at a pressure of 40 Kgf/cm ² for 20 seconds.

Third step: Raise the temperature without applying pressure.

Fourth step: After reaching 150, a pressure of 40Kgf/cm ² is applied, then the temperature is raised to 180℃ and held for 60 minutes.

Among the five pairs of insulating substrates obtained through the above process, the thickness of the insulating layer of the first, third, and fifth insulating substrates was measured over the entire surface (every 10 mm in both the vertical and horizontal directions). Figure 2 shows the results. A uniform insulating layer is formed over the entire surface with a thickness variation of less than 3 μm.

Example 2 The materials shown in Example 1 were used except for the adhesive with a gelling time (@160°C) of 47 seconds and one cushion material for each upper and lower layer, and the heat and pressure treatment conditions were also implemented. An insulating substrate was produced under the same conditions as in Example 1. The results of measuring the thickness of the insulating layer of the obtained substrate (third stage) are shown in FIG. The variation in the thickness of the insulating layer in the first, third, and fifth stages (excluding 1/5 from the end) at measurement points 36 was 8 μm for each stage. Although the thickness at the end portions is smaller than in Example 1, the thickness at the center portion is approximately uniform.

Comparative Example 1 A substrate was fabricated using the adhesive used in Example 2 and the metal foil and metal plate used in Example 1, while heating and pressurizing was performed only in the fourth step of Example 1. The thickness variation within the portion excluding the 1/5th from both ends of the insulating layer of each stage was as follows.

1st stage: 16μm, 3rd stage: 8μm, 5th stage:
20μm. FIG. 4 shows the measurement results of the thickness of the insulating layer at each position on the fifth stage insulating substrate. It is understood that the thickness of the end portions is thinner than that of the center portion, and that the thickness variation of the center portion also becomes larger.

[Effects of the Invention] As shown above, by controlling the heating and pressing method of the adhesive layer under the specific conditions of the present invention, for the first time, it is possible to uniformly and sufficiently cover the entire surface of the substrate using only the adhesive layer without using prepreg. Because it is possible to stably form a thin insulating layer (adhesive layer) on the substrate, it has become possible to produce heat dissipating electrically insulating substrates for printed circuits with excellent heat dissipation and electrical insulation properties at a high yield.

[Brief explanation of drawings]

FIG. 1 shows an example of a profile showing how to apply temperature and pressure with respect to time in the second to fourth steps in the method of the present invention. When the sample temperature is 5°C or lower than the softening point of the adhesive, pressurize _P1 for a short time at _T1 , then after increasing the temperature, pressurize at _T2 in the temperature range from the gelation end point of the adhesive to 30°C higher than that. _P2
and then pressurization at T ₃ at a constant temperature. Note that T(g) indicates the temperature at the end point of gelation, and T(g+30) indicates a temperature 30° C. higher than the end point of gelation. FIGS. 2 and 3 show the thickness of the insulating layer in the vertical and horizontal directions of the insulating substrate manufactured by the method of the present invention. FIG. 4 shows the thickness when only _P2 pressure is applied without performing _P1 .

Claims (1)

[Claims] 1. A method for manufacturing a heat-dissipating electrically insulating substrate by stacking and heat-treating multiple pairs of metal plates stacked on a metal foil coated with an epoxy resin adhesive uniformly, comprising: (a ) The first step is to uniformly apply an epoxy resin adhesive to the metal foil in advance and then heat treat it to bring it to a B-stage state. Pressure is applied for a period of time, and the B-
A second step of physically adhering the adhesive layer in the stage state to the metal plate without softening and deforming it; (c) increasing the temperature without applying pressure to the extent that the adhesive layer maintains its initial thickness without deforming; (d) From the end point of gelation of the adhesive to the end point of gelation.
When it reaches a temperature range 30℃ higher, it is pressurized again and then pressurized at a constant temperature.
A method for manufacturing a heat dissipating electrical insulating board, comprising: a fourth step of completely curing the adhesive layer while preventing deformation of the adhesive layer and adhering it to a metal plate. 2. In the second step of the preceding paragraph (b), when performing pressure treatment, the temperature is at least 5 % above the softening point of the adhesive.
2. The method for manufacturing a heat dissipating electrically insulating substrate according to claim 1, wherein a pressure treatment is carried out for 10 to 30 seconds at a pressure of 30 to 50 Kgf/cm ² (G) at a temperature lower than or equal to .degree. 3. Claims 1 or 2 in which the metal foil is any one of copper foil, aluminum foil, or nickel foil, and the metal plate is any one of aluminum plate, iron plate, aluminum alloy plate, or iron-based alloy plate. 2. A method for manufacturing a heat dissipating electrically insulating substrate according to item 2. 4 Gel time of epoxy resin at 160℃ 10 to 30
The method for manufacturing a heat dissipating electrically insulating substrate according to claims 1 to 3, wherein