JPH0817267B2 - Substrate for high frequency circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a substrate for electronic equipment, and particularly to a high-frequency circuit substrate suitable for use in a high-frequency region.

[Conventional technology]

The frequencies of signals used in recent fields of electronics industry and communication industry are gradually shifting to the high frequency region, and the importance is shifting from the conventionally frequently used region of kilohertz to the region of megahertz and gigahertz. . In these high-frequency regions, the signal speed and the loss of signals have a great influence on the circuit performance, and there is a demand for improvement of the signal speed and reduction of the loss in the high-frequency region for the electric components and laminated plates used. The signal speed of the circuit on the laminate depends on the relative permittivity (hereinafter referred to as εr) of the dielectric of the laminate, and the lower εr, the faster the signal speed. Also, the signal loss depends on the εr and ta of the dielectric.
It depends on nδ (δ: dielectric loss angle), and the loss decreases as εr and tanδ decrease. Therefore, the dielectric used for the high frequency substrate is required to have a low εr or tanδ. A glass cloth impregnated with a resin such as polytetrafluoroethylene or polyethylene is used as a dielectric material having a low εr or tan δ, and a high frequency substrate in which a copper foil is laminated on this is generally used.

[Problems to be Solved by the Invention]

The glass cloth substrate of polytetrafluoroethylene, which uses a dielectric material in which glass cloth is impregnated with polytetrafluoroethylene, has a high melting point and low flowability of polytetrafluoroethylene. However, there is a problem that the cost becomes high. On the other hand, polyethylene / glass cloth impregnated with polyethylene /
Since the glass cloth substrate has a low melting point of polyethylene, it has a defect of poor soldering heat resistance.

[Means for solving the problem]

In order to improve these points, the inventors of the present invention disclosed in JP-A-3-109791 and JP-A-3-109792 that a porous sheet of ultra-high molecular weight polyethylene (hereinafter sometimes referred to as UHMWPE) was not used as a porous sheet. A method of manufacturing a substrate for a high-frequency circuit, in which a reinforcing layer (hereinafter also referred to as a prepreg) impregnated with a curable resin for curing is laminated, and heat and pressure are applied to lose porosity and at the same time, the curable resin is cured. Proposed. This is because, while taking advantage of the low εr and low tanδ of UHMWPE, the heat resistance is improved by the low fluidity at the time of melting and the process difficulty is overcome by laminating the prepreg and the UHMWPE porous sheet.

However, if the melt viscosity of the uncured curable resin used for the prepreg exceeds 3000 poise, the penetration into the UHMWPE porous layer is only the surface layer, and if the through hole is plated without surface treatment, there is no There was a problem that the plating would peel off on the wall surface of the flexible UHMWPE. In addition, since the thermal expansion amount of UHMWPE and the curable resin in the flat plate direction due to the heat of the solder when mounting the components is different, there is a drawback that the plated copper in the through hole is cracked at the interface.

Note that the melt viscosity of the uncured curable resin used for the prepreg here is a sample of the prepreg that is crushed so that the reinforcing layer does not break, and the resin powder that has fallen from the prepreg is sifted through a 100-mesh sieve. And flow tester (Shimadzu CF tester manufactured by Shimadzu Corporation)
T-500C) is the minimum viscosity when measured at a temperature of 130 ° C and a load of 3 kg.

The present invention has been made in view of the above circumstances, and provides a substrate for a high-frequency circuit that has heat resistance, is easy to process, and has good adhesion and conduction reliability in through-hole plating. is there.

As a result of repeated intensive studies to solve the above-mentioned problems, the inventors of the present invention used a substrate in which a cured epoxy resin-impregnated reinforcing layer and a metal conductor layer are laminated on a sheet in which a cured epoxy resin is dispersed in UHMWPE. The inventors have found that the above problems can be solved, and have completed the present invention based on this finding.

That is, the present invention is characterized in that a cured epoxy resin-impregnated reinforcing layer is laminated on both sides or one side of a sheet in which a cured epoxy resin is dispersed in ultrahigh molecular weight polyethylene, and further a metal conductor layer is provided. The present invention provides a substrate for a high frequency circuit.

Hereinafter, the present invention will be described in detail with reference to the drawings. First
The figure shows that a through hole is provided in the high-frequency circuit board of the present invention,
It is a sectional view of what plated copper is given to the substrate surface and the inner wall of a through hole. Figure 2 shows that the cured epoxy resin is UHMW
FIG. 3 is a cross-sectional view of a high-frequency circuit substrate that is not dispersed in PE. As shown in Fig. 1, there is a portion where the plated copper 1 is in contact with the cured epoxy resin 5 that has better adhesion to copper than UHMWPE4 even in the center of the inner wall of the through hole, so that adhesion to the plated copper is secured over the entire inner wall. It 3 and 4 are cross-sectional views when the substrate shown in FIGS. 1 and 2 is heated. Comparing the difference in the amount of thermal expansion between UHMWPE in the flat plate direction and the cured epoxy resin-impregnated reinforcing layer when heat is applied to the substrate, in Fig. 3 the cured epoxy resin in UHMWPE suppresses thermal expansion. ₁ <Δl ₂ , and
The amount of deformation at the interface of the plated copper becomes smaller. Therefore, the substrate of FIG. 3 has improved conduction reliability.

The high-frequency circuit substrate of the present invention, for example, a reinforcing sheet (hereinafter sometimes referred to as prepreg) in which an epoxy resin having a melt viscosity of 3000 poise or less is impregnated on both surfaces or one surface of a porous sheet of ultra-high molecular weight polyethylene. Stacked
Further, it can be manufactured by laminating a metal conductor layer, heating and pressing the metal conductor layer to eliminate the porosity of the porous sheet, and at the same time infiltrating the uncured epoxy resin into the porosity to cure.

Examples of the prepreg include those obtained by impregnating and drying an epoxy resin varnish on a reinforcing material such as glass cloth, glass non-woven cloth, plastic fiber woven cloth, non-woven cloth and the like which are usually used for printed circuit boards. If the melt viscosity of the epoxy resin is less than 3000 poise, the epoxy resin is sufficiently impregnated into the UHMWPE porous interior by heating and pressing when creating the substrate, and the epoxy resin is dispersed in the UHMWPE as shown in Fig. 1. The obtained structure can be obtained. The amount of prepreg used is preferably 50 to 200 g / m ² , and the thickness of the reinforcing layer is 30 to 200.
μm is preferred.

UHMWPE used for the porous sheet of ultra-high molecular weight polyethylene of the present invention is produced by the Ziegler method polymerization technology, and its average molecular weight is 1-5 million as measured by the viscosity method and 20,000-200,000 of general polyethylene. It has an extremely large molecular weight. For example, those commercially available from Mitsui Petrochemical Industry (Hi-Zex Million, Miperon), Asahi Kasei Kogyo (Suntech), West German Hoechst Company (HOSTALEN.GUR), USA Hercules Company (HIFAX.1000) and the like are preferably used.

The UHMWPE porous sheet sinters UHMWPE powder particles,
The particles are fused together to form a sheet having a thickness of 0.5 to 5 mm. There is a continuous layer of air outside the bonded particles.

UHMWPE porous sheet manufacturing method, for example, a film,
Put powder particles of UHMWPE on a base material such as a metal belt,
This is passed through the obtained distance by keeping the distance between them and the substrate constant with a roll or bar to shape the UHMWPE powder particles to a certain thickness, and then passed through a heating furnace to heat and sinter the particles. , UHMWPE porous sheet can be continuously formed. At this time, the UHMWPE powder particles may be coated with an adhesive, or particles having adhesiveness, a stabilizer, a flame retardant, a coloring agent, etc. may be added.

The UHMWPE powder preferably has an average particle size of 0.001 to 1 mm. In order to make the surface of the obtained UHMWPE porous sheet smooth, it is particularly preferable that the average particle size is 0.001 to 0.1 mm.

The metal conductor layer is a foil or plate of copper, copper alloy, aluminum, nickel, iron, iron alloy, stainless steel, gold, silver, platinum or the like. Preferred are copper foil, aluminum foil, aluminum plate, and iron alloy plate. Further, plating for forming a predetermined circuit may be used instead of the metal foil or plate. Their thickness is usually 10 to 50 μm.

The heating and pressurizing conditions are usually 130 to 250 ° C, and the applied pressure is 20 to 20 ° C.
It is preferable to perform the heating at 80 kg / cm ² (2.0 to 7.8 MPa) for 20 to 120 minutes, sandwich the UHMWPE porous sheet, prepreg and metal sheet between the end plates and heat and pressurize under uniform conditions.

[Action]

Since the epoxy resin is dispersed in the UHMWPE, the high-frequency circuit substrate of the present invention suppresses the amount of thermal expansion of UHMWPE in the flat plate direction, reduces the thermal expansion difference at the interface with the prepreg, and improves the reliability of through-hole conduction. It seems that the sexuality is improved. Further, since the epoxy resin having good adhesion to the plated copper is dispersed on the inner wall of the through hole, it is considered that the adhesion to the plated copper is secured on the entire inner wall.

〔Example〕

Hereinafter, the present invention will be described in detail based on Examples,
The present invention is not limited to this.

Example 1 Miperon XM220 as UHMWPE (average particle size 0.03 mm, melting point 136 ° C., bulk density 0.4 g / cm ³ , true density of polyethylene 0.94 g
/ cm ³ , Mitsui Petrochemical Co., Ltd. product name) is shaped on a glass plate to a thickness of 0.8 mm, and sintered by heating in a heating furnace at 160 ° C for 20 minutes to give an apparent density of 0.5 g / cm ³ of UHMWPE. A porous sheet of

Two sheets of this porous sheet were stacked, and brominated bisphenol A with a melt viscosity of 2000 poise was applied to both sides of glass cloth with a thickness of 60 μm.
35 μm-thick electrolytic copper foil (Furukawa Circuit Foil Co., Ltd.) was laminated through a prepreg (resin content 60% by weight) impregnated with a type epoxy resin (Tg130 ° C.), and a stainless steel end plate was used at 175 ° C. The substrate was heated and pressed for 90 minutes under the condition of 40 kg / cm ² to obtain a high-frequency circuit substrate having a thickness of 0.95 mm.

Comparative Example 1 A prepreg impregnated with an epoxy resin having a melt viscosity of 4000 poise was used in the same manner as in Example 1 to obtain a thickness of 0.
A 95 mm high frequency circuit board was obtained.

The cross sections of the above two types of high frequency circuit substrates were observed with a scanning electron microscope. In the example, the epoxy resin was dispersed up to the center of UHMWPE, whereas in the comparative example, dispersion up to 0.25 mm from the interface was observed, but the center was UHMWPE.
It was only PE.

In addition, the test pattern conforming to JIS C5012 was used to drill holes, and electroless copper plating solution CUST201 (trade name of Hitachi Chemical Co., Ltd.) was used to perform plating of 0.5 μm thick, followed by copper sulfate electroplating to 40 μm thick. Plating,
A sample with through-hole plating was obtained. At this time, the adhesion of plating was sufficient in Example 1, but in Comparative Example 1, peeling occurred on the wall surface with UHMWPE. Plating became possible even in Comparative Example 1 by the chromic acid / sulfuric acid mixed solution treatment at 60 ° C. for 2 hours. Therefore, a test pattern was formed on the through-hole plated sample treated in both the Example and Comparative Example, and the plating through was performed. Withdrawal strength test of the hole,
A thermal shock test was performed using 260 ° C. oil. The results are shown in Table 1.

In Example 1, the adhesion and conduction reliability of through-hole plating are greatly improved.

In order to investigate the effect of suppressing thermal expansion, UHMWPE only, a sheet of epoxy resin only, and prepreg of the epoxy resin used in the examples and impregnated with a varnish of the epoxy resin to the same fraction as the substrate of the example, The amount of thermal expansion in the flat plate direction of the epoxy resin-dispersed UHMWPE sheet obtained by pressing,
Each was measured by a thermomechanical analyzer (TMA8140 manufactured by Rigaku Denki) (20 ° C to 260 ° C). Based on this value, the thermal expansion amount of the 5.08 mm sample, which is the same as the spacing between the through holes of the test pattern, was calculated. The results are shown in Table 2.

In the laminated body of the prepreg and the UHMWPE sheet, the numerical values in Table ₂ do not directly represent the difference in the strain in the plate direction at the interface (Δl ₁ and Δl _{2 in} FIGS. 3 and 4). However, the smaller the amount of thermal expansion of the sheet, the smaller the difference in strain at the interface with the prepreg. Therefore, epoxy resin dispersion
By using the UHMWPE sheet, it is possible to reduce the amount of deformation of the plated copper on the inner wall of the through hole and improve the conduction reliability.

〔The invention's effect〕

According to the present invention, since the epoxy resin is dispersed in UHMWPE, the adhesion of through-hole plating is good, and the thermal expansion of UHMWPE in the flat plate direction is suppressed, so that a substrate having good conduction reliability can be obtained. it can. Further, by using an epoxy resin having a melt viscosity of 3000 poise or less for the prepreg, it is possible to manufacture a substrate in which the cured epoxy resin is dispersed in UHMWPE.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of a substrate for high-frequency circuits according to the present invention, and FIG. 2 is a substrate when through-hole plating is applied to a substrate on which a cured epoxy resin is not dispersed. Further, FIGS. 3 and 4 are respectively FIGS.
It is a fragmentary sectional view showing typically thermal expansion when heat is applied to the substrate of a figure. Explanation of symbols 1 ... Plated copper, 2, 2 '... Metal conductor layer 3, 3' ... Hardened curable resin impregnated reinforcing layer 4 ... Ultra high molecular weight polyethylene 5 ... Hardened epoxy resin

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yutaka Yamaguchi 1500 Ogawa, Shimodate, Ibaraki Prefecture Shimodate Laboratory, Hitachi Chemical Co., Ltd. (56) Reference JP-A-1-173695 (JP, A) JP-A-63 -237948 (JP, A)

Claims (1)

[Claims] 1. A reinforcing sheet, which is uncured and is impregnated with an epoxy resin having a melt viscosity of 3000 poise or less, is laminated on both sides or one side of an ultrahigh molecular weight polyethylene porous sheet, and a metal conductor layer is further laminated and heated. Both sides of the sheet formed by dispersing the cured epoxy resin in ultra-high molecular weight polyethylene by applying pressure to eliminate the porosity of the porous sheet and at the same time infiltrating the uncured epoxy resin into the porous body and curing it A substrate for a high-frequency circuit, characterized in that a cured epoxy resin-impregnated reinforcing layer is laminated on one side, and a metal conductor layer is further provided.