JPH0564879B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for obtaining a laminate suitable as a material for metal-based printed wiring boards. (Prior art) Metal-based printed wiring boards consist of a metal core board and a conductive circuit layer provided on its surface with an insulating layer interposed between them.It has excellent heat dissipation and magnetic shielding properties, and is suitable for use in hybrid IC boards, etc. It is used for various purposes. Conventionally, as shown in the cross-sectional view of FIG. 3, the laminated board that is the raw material for this metal-based printed wiring board is made of epoxy resin-impregnated glass fiber mat (glass It was common to heat-press epoxy 3' to cover the surface of the core plate 1, and at the same time, flow the epoxy resin in the glass epoxy into the holes 11 to cover the surfaces of the holes 11. . (Problems to be Solved by the Invention) However, in a laminated board in which the core plate is coated with glass epoxy, air bubbles 12 tend to remain on the surface of the holes 11, resulting in poor insulation when a through hole is made in the hole 11. It had become a serious drawback. Furthermore, glass epoxy does not have sufficient high frequency characteristics, and depending on the application, even higher performance has been desired. In order to solve the above problems, the present inventors investigated a method of covering the metal core plate, including the hole surface, with a highly heat-resistant thermoplastic resin. However, in cases where even higher quality is required, it is still far from perfect. (Means for Solving the Problems) The present invention produces a laminate with extremely few remaining bubbles by hot pressing a heat-resistant thermoplastic resin film and a metal core plate provided with through holes in a reduced pressure atmosphere. It was successfully obtained. The present invention will be described in detail below with reference to the drawings. FIG. 1 is a sectional view showing an example of a laminate obtained by the method of the present invention, and FIG. 2 is a sectional view showing another example. The one shown in Figure 2, which is coated and insulated with a plastic resin film 2 and has a conductive circuit on its surface, is further coated with a prepreg layer 3 made of glass epoxy or the like.
A conductive circuit is provided on this layer 3. The metal core plate used in the present invention is provided with a large number of through holes 11 in advance, and usually has a thickness of about 0.1 to 1.6 mm. Materials include iron, aluminum, copper,
There are zinc, etc. This core plate 1 has been subjected to surface roughening treatments such as sandblasting, liquid honing, and etching to improve the surface roughness (center line average roughness specified by JIS B 0601).
Preferably, the surface is finely roughened to a diameter of 1 μm or more and 12 μm or less, particularly 1.2 μm or more. This is thought to be due to the fact that air between the layers easily escapes during hot pressing, and the anchoring effect of the rough surface combines to increase the adhesive strength. At the same time, alumite treatment, alodine treatment,
It is preferable to perform a treatment such as resin coating to improve the adhesive strength. As the heat-resistant thermoplastic resin film 2, a thermoplastic resin that is resistant to soldering heat, such as a film made of polysulfone, polyetheretherketone, polyphenylene sulfide, etc., can be used. / ^cm2 ) is
A film made of a resin having a temperature of 200° C. or higher, such as polyetherimide (200° C.), polyether sulfon (203° C.), or polyamideimide (274° C.) is preferred. The thickness of the film 2 is preferably about 0.25 to 0.5 mm, taking into account the reduction in thickness during lamination. In order to laminate the core plate 1 and the film 2, they are placed on top of each other and heated and pressed under reduced pressure. The degree of pressure reduction (difference between normal pressure and residual pressure) is 600 mmHg or more, preferably 650 mmHg or more. If the degree of pressure reduction is lower than this, the air bubbles will not be completely removed. When heat pressing is performed under normal pressure, air bubbles remain in the pores and between the layers, and not only are these air bubbles not easily removed even when high temperature and pressure are applied, but the film 2 may flow out or undergo thermal deterioration due to the harsh heat and pressure bonding conditions. disadvantages arise. However, when hot pressing is carried out under reduced pressure conditions of approximately 600 mmHg, most of the air between the layers and in the pores is easily released while the film 2 is in a solid state, unlike films that contain liquid components such as glass epoxy. Moreover, since pressure is constantly applied to the resin, noticeable air bubbles are almost invisible. It also has the great effect of providing high adhesive strength by suppressing oxidation of the surface of the metal core plate due to heating during pressing. Here, the heating temperature needs to be in the range above the flow start temperature of the resin constituting the film 2 and below the thermal decomposition temperature, so it naturally varies depending on the material of the film 2, but in general, it is less than 200°C. The adhesive force between the core plate 1 and the film 2 is weak, and if the temperature exceeds 450°C, the film 2 will flow and the thickness will decrease significantly, which is not preferable, so the temperature should be in the range of 200 to 450°C.
Preferred temperatures are, for example, 350-380°C for polyetherimide, 320-350°C for polyethersulfone, and 280-340°C for polysulfone.
℃, for polyamideimide it is in the range of 300 to 400℃, and for polyetheretherketone it is in the range of 350 to 380℃. Within these ranges, by selecting an appropriate pressing pressure, the film 2 will not flow out significantly during pressing, and the film 2 will melt and a part of it will flow into the hole 11 and fill it. Good results are obtained since the surface is well covered. In addition, the press pressure should preferably be in the range of 50 to 200Kg/ ^cm2 .
If this is less than 50 kg/cm ² , air bubbles between the layers and in the pores will not be removed sufficiently even under reduced pressure, and the adhesive strength will be weak.
If it exceeds Kg/cm ² , the thickness of the film 2 will be reduced unnecessarily, making it impossible to obtain a laminate with a predetermined thickness. Practically speaking, sufficient adhesive strength can be obtained with a pressure of about 100 kg/cm ² . Once the heating press is completed, cooling begins. It is preferable to pressurize during this cooling, but it is not necessarily necessary to maintain reduced pressure. Figure 2 shows a laminate with a particularly preferred configuration. When obtaining such a laminate, an uncured prepreg such as glass epoxy and, if necessary, a conductive material such as copper foil may be added on the film layer 2. The metal foils may be stacked and pressed at a temperature of about 120 to 200°C and a pressure of 5 to 150 kg/cm ² . In this case, it is not necessary to carry out the process in a reduced pressure atmosphere. If the temperature is lower than 120°C, the adhesive strength will be weak, and if it exceeds 200°C, thermal decomposition of the resin in the prepreg will easily occur, which is not preferable. The time is 10 minutes or more so that the resin in the prepreg is sufficiently cured. Prepreg 3 is made of epoxy resin, phenolic resin, polyester resin, etc. on mat such as glass fiber.
It is impregnated with a thermosetting resin such as allyl resin, and is preferably used by stacking several sheets with a thickness of about 0.1 to 0.2 mm. Providing the prepreg layer 3 on the surface of the laminate in this way improves the surface smoothness by compensating for the tendency of thermoplastic films to cause "sink marks", and also improves the heat-resistant dimensional stability, solvent resistance, etc. of the insulating layer. improves. Example 1 The following two types of metal core plates were prepared, each having a large number of through holes with a diameter of 0.5 to 5 mm. (a) 1.6mm thick aluminum plate (surface roughness 1.2μ, alodine treatment) (b) 1.6mm thick aluminum plate (surface roughness 0.2μ, alodine treatment) Thickness is applied to both sides of these core plates. Layering polyetherimide films with a diameter of 0.3 mm and changing the atmospheric pressure,
It was heated and pressed for 90 minutes at a press pressure of 100 kg/cm ² , and then cooled while being pressurized. Next, two glass epoxy sheets each having a thickness of 0.1 mm were stacked on both sides of the resin layer, and pressed at a temperature of 170° C. and a pressure of 50 Kg/cm ² for 10 minutes (in a normal pressure atmosphere) to obtain a laminate. Then, cut the resin inside the hole to create an opening.
The surface is observed under a microscope to check for the presence of air bubbles.
Those without bubbles with a diameter of 2 μm or more were marked as ○, and those with bubbles were marked as ×. In addition, the adhesion strength between the core plate and film is determined by JIS
Measured by C6481. The results are shown in Table 1.

[Table] As is clear from the above results, do not depressurize
No. 4 and No. 3 with insufficient degree of vacuum do not allow sufficient air bubbles to escape, but no air bubbles remain on the pore surface with those made by the method of the present invention (Nos. 1 to 2 and 5), which are heat-pressed under reduced pressure. . In addition, to obtain high adhesive strength,
It can be seen that a surface-roughened plate is preferable as the core plate. Example 2 Aluminum core plate (a) whose surface was treated with sulfuric acid alumite
(Surface roughness 1.3 μm) Layer 0.3 mm thick polyether sulfon film on both sides and press 75 at 330℃ and press pressure 100Kg/cm ² in 600mmHg atmosphere.
Heat pressed for a minute. Next, glass epoxy was laminated on both sides of the resin layer in the same manner as in Example 1 to obtain a laminate having the structure shown in FIG. 2. The laminate had no air bubbles, sufficient adhesion between the layers, and a smooth surface. (Effects of the Invention) According to the present invention, a laminate can be obtained that is free of air bubbles not only on the surface of the core plate but also in the pores where bubbles have conventionally remained significantly.

[Brief explanation of the drawing]

1 and 2 are sectional views showing an example of a laminate obtained by the method of the present invention, and FIG. 3 is a sectional view showing a conventional laminate. DESCRIPTION OF SYMBOLS 1...Metal core plate, 11...Through hole, 2...Heat-resistant thermoplastic resin layer, 3...Prepreg.

Claims (1)

[Claims] 1. A heat-resistant thermoplastic resin film and a metal core plate having through holes are heated at a temperature of 200 to 450°C and a pressure of 50 to 300°C in a reduced pressure atmosphere with a degree of reduced pressure of 600 mmHg or more.
1. A method for producing a metal base laminate, comprising heating and pressing under conditions within a range of Kg/cm ² to cover the surface of the core plate with the resin and filling the through holes. 2. The method according to claim 1, wherein a finely roughened plate having a surface roughness of 1 μm or more is used as the metal core plate.