JPH0444385A - Manufacture method of high frequency substrate - Google Patents

Abstract

PURPOSE:To lower the value of tan delta and protect a substrate from warping or dimensional change by allowing the apparent density of a porous sheet to exceed a specified value, carrying out heat treatment for a crosslinked polymeric polyethylen sheet at or above a specified temperature, and then laminating metal foil or metal sheets on both sides or one side of this sheet. CONSTITUTION:A HMWPE porous sheet containing a cross linking agent is pressure- heated while its porous quality may be eliminated so that the apparent density of the porous sheet may exceed 80% of the genuine density. At the same time, the crosslinked polymeric polyethylene sheet obtained from cross linking processing is heat-treated at a temperature of 260 deg.C. Then, after the heat treatment, metal foil or metal sheets are laminated on both sides or one side of the sheet directly or indirectly by way of a bonding layer or a resin impregnated reinforcing layer. When the apparent density is less than 80% of the genuine density of HMWP, epsilonr or tan delta is lower and favorable, but the open cells remain so that liquid may penetrate into the sheet, which adversely affects the characteristic of a substrate where the porous quality is eliminated by a specified value and over and cross linked while the HMWP sheet is heat-treated at a temperature of 260 deg.C and over. More favorably, heat treatment is carried out at a temperature which ranges from 260 to 300 deg.C.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a high-frequency substrate used in a high-frequency region [Prior Art] The frequency of signals used in recent electronic and communication industries has gradually increased. Moving into the high frequency range, importance is shifting from the conventional kilometer range to the megahertz and gigahertz range. In these high frequency ranges, signal speed and signal loss have a large effect on circuit performance, and there is a need for the electrical components and laminates used to increase signal speed and reduce loss in the high frequency range. The signal speed of the circuit on the laminate is determined by the relative permittivity of the dielectric 'V=(
(hereinafter referred to as ε), and the lower ε, the faster the signal speed. Also, the signal loss is caused by the dielectric's ε1 and ta.
It depends on nδ (δ: for dielectric devices), and ε, and tan
The lower the δ, the lower the loss. For this reason, dielectrics used in high frequency substrates are required to have low ε and anδ. A glass cloth impregnated with a resin such as polytetrafluoroethylene or polyethylene is used as a dielectric material with low ε1 and tan δ, and a high frequency board made of a copper foil laminated thereon is generally used.

Polytetrafluoroethylene/glass cloth substrates using a dielectric material made of glass cloth impregnated with polytetrafluoroethylene require long-time molding at high temperatures due to the high melting point and low fluidity of polytetrafluoroethylene. There was a problem that the cost was high. On the other hand, polyethylene/glass cloth substrates in which glass cloth is impregnated with polyethylene have a drawback of poor solder heat resistance because the melting point of polyethylene is low.

For improvement in these points, for example, Japanese Patent Application Laid-Open No. 60-25352
As shown in Publication No. 8, a polyethylene film is placed on both sides of a glass cloth, heated and pressed to impregnate the glass cloth with polyethylene, crosslinked with an electron beam, and then copper foil is laminated to form a substrate. As shown in JP-A-61-108202, JP-A-61-277207, and JP-A-61277208, glass cloth is impregnated with polyethylene by heating and pressurized, and then a polyethylene film is further layered. A method has been proposed in which a polyethylene film is cross-linked with an electron beam after thermocompression bonding, and a substrate is manufactured by laminating an ultra-high molecular weight polyethylene film cross-linked with an electron beam and a copper foil thereon. In this way, the heat resistance of polyethylene is basically improved by crosslinking the polyethylene to reduce the fluidity of the resin.

For the purpose of improving heat resistance, it is sufficient to use ultra-high molecular weight polyethylene (hereinafter sometimes referred to as HMWPE), which has low resin fluidity, but like polytetrafluoroethylene, HMWPE has a low viscosity when melted by heating. Due to its high price, it has the disadvantage that ordinary extrusion molding methods and injection molding methods are difficult to adapt to.

For this reason, the method for forming HMWPE sheets and films is as in the case of polytetrafluoroethylene: HMWPE is charged into a double cylindrical container, heated and pressurized to a temperature above the melting point of HMWPE, and then slowly cooled to form a pipe-shaped block of HMWPE. The method used is to form the material and cut it into sheets or films using a skiving machine. However, with this method, the temperature and pressure must be delicately adjusted to avoid voids when forming the HMWPE block, and the temperature of the HMWPE block must be heated to the appropriate temperature for cutting. Conditions need to be strictly controlled. Another problem is that the hatch method is a molding method that is not suitable for mass production.

[Problem to be solved by the invention]

As a result of intensive research, the present inventors have improved the moldability of the high-frequency substrate by using a polymer made of ultra-high molecular weight polyethylene (HMWPE), which has small ε and tan δ and good dielectric properties, as the dielectric material of the high-frequency substrate. To do, -dan HM
It has been found that the object can be achieved by manufacturing a porous sheet of WPE and further heating and pressing this sheet to form a sheet of HMWPE having a uniform thickness. Furthermore, in order to make a high-frequency substrate with extremely excellent heat resistance, a crosslinking agent was added to the HMWPE porous sheet as a means of crosslinking the HMWPE, and the porous sheet was heated and pressed to increase the apparent density to HMWPE.
The porosity is eliminated so that the true density of MWP E becomes 80% or more, and at the same time a crosslinking treatment is performed to make the crosslinking [(MWP
We proposed a method for manufacturing a high-frequency substrate in which an E sheet is formed and a metal foil or metal plate is laminated on the obtained sort directly or via an adhesive layer or a resin-impregnated reinforcing layer (Japanese Patent Application Laid-Open No.
-248428). However, although the heat resistance of the obtained substrates is improved, the substrates that are crosslinked with a crosslinking agent (peroxide crosslinking, run crosslinking) have a higher ε than those that are not crosslinked or those that are crosslinked with electron beams.

were almost the same, but tan δ tended to show a high value. In addition, only HMWPE components can be used in solder baths, etc.
When exposed to an atmosphere at a temperature of
This is inherent in the MWPE sheet, and when it is molded into a substrate, there is an inherent problem that it causes large warpage and dimensional changes, causing blistering.

An object of the present invention is to provide a method for manufacturing a high-frequency substrate that has a significantly low tan δ value, does not warp or change dimensions during molding, and does not cause bulges on the substrate.

[Means for Solving the Problems] The present inventors investigated the increase in tan δ and the dimensional change upon heating when a crosslinking agent was added to the above-mentioned HMWPE and crosslinked it, and as a result, the crosslinked HMWPE sheet was By heat treatment at temperatures above °C, tan
It was discovered that δ was significantly reduced and dimensional changes in the substrate during molding could be reduced, and based on this knowledge, the present invention was completed.

That is, the present invention was obtained by heat-pressing a porous sheet of HMWPE containing a crosslinking agent to eliminate porosity and simultaneously perform a crosslinking treatment so that the apparent density of the porous sheet becomes 80% or more of the true density. It is characterized by heat-treating a cross-linked ultra-high molecular weight polyethylene sheet at a temperature of 260°C or higher, and then laminating metal foil or metal plate on both sides or one side of the sheet, either directly or via an adhesive layer or a resin-impregnated reinforcing layer. A method for manufacturing a high frequency substrate is provided.

The HMWPE used in the ultra-high molecular weight polyethylene porous sheet of the present invention is produced by Ziegler polymerization technology, and its average molecular weight is 1 million to 100% as measured by the viscosity method.
It has an extremely large molecular weight of 5 million, compared to 20,000 to 200,000 for general polyethylene. For example, Mitsui Petrochemical Industries (Hyzex Million, Miperon), Asahi Kasei (Santic), West German Hoechst (HO3TAL),
EN, GtJR), U.S. Percules Inc. (HI FA)
X, 1000) or the like is preferably used.

HMWPE porous sheets are made by sintering HMWPE powder particles, joining the particles by fusion, and forming a sheet with a thickness of 0.5 to 5 mm.
It is molded into a sheet of n. There is a continuous layer of air outside the bonded particles.

A method for manufacturing a porous sheet of HMWPE is to place HMWPE powder particles onto a base material such as a film or a metal belt, and then use rolls or bars to maintain a constant distance between them and the base material. There is a method of continuously forming a porous sheet of HMWPE by passing the HMWPE powder particles through a heating furnace to form them into a constant thickness, and then passing them through a heating furnace to heat and sinter the particles. At this time, the HMWPE powder particles may be coated with an adhesive, or particles having adhesive properties, a stabilizer, a flame retardant, a coloring agent, etc. may be added.

HMWPE powder has an average particle size of 0. It is preferable that the cylinder has OO1 to 1. In order for the surface of the obtained HMWPE porous sheet to be smooth, the average particle diameter must be 0.0 O.
1 to 0.1 trm is particularly preferred.

A porous sheet of HMWPE has a cellular structure due to the fusion of powder particles, and the cellular structure is open cells. At this time, if the sintering is further progressed, the fusion progresses and the sheet finally becomes a sheet containing a small amount of closed cells. However, in the present invention, since the porosity is eliminated by heating and pressurizing, it is preferable that the cell structure is an open cell structure so that bubbles can be easily removed during heating and pressurizing. In order to obtain an open cell structure, adjust the heating temperature and heating time during sintering, and
The apparent density of the porous sheet of WPE may be less than 80% of the true density of the HMWPE powder particles. Since the thickness of the porous sheet of HM W P E is determined by equation (1), it is advisable to adjust the spacing to obtain the desired thickness.

Thickness of porous sheet of HMWPE - ((tried to obtain) (thickness of M W P E dielectric sort) x (] iMWPE true density)) / (HMWP
Considering the dimensional change (E porous sheet polishing density) and assuming that it shrinks in the surface direction and increases in thickness in the thick direction by the amount of shrinkage, multiply the right side of equation (1) by (1 - dimensional shrinkage rate) XI/2. It's good to know.

The crosslinking agent crosslinks polyethylene, and is crosslinked by a peroxide crosslinking method or a silane crosslinking method, which are commonly used as methods for crosslinking polyethylene.

For example, in the peroxide crosslinking method, an organic peroxide that generates an radical site may be added. Examples of organic peroxides include 2,5-dimethyl-25-di(t-butylperoxy)hexyne-3, methyl ethyl ketone peroxide, t-butylperoxy-2-ethylhexanoate, cumene hydroperoxide, 2, 5-dimethyl-
2゜5-di(t-butylperoxy)hexane, 6゜6
．． 9.9-Tetramethyl-3-methyl-3-n-butyl-1,2,4,5-tetraoxycyclononane, dicumyl peroxide, t-butylperoxyperbenzoate, t-butylperoxyisopropyl carbonate, etc. can be mentioned. In addition, organic peroxides and divinylbenzene, triallyl cyanurate, triallyl isocyanurate, trimethylolpropane triacrylate, p, P
A polyfunctional compound (crosslinking aid) such as dibenzoylquinone dioxime may be used in combination.

In the silane crosslinking method, the general formula RR'5iYz (where R is a monovalent olefinic unsaturated hydrocarbon group, Y is a hydrolyzable organic group such as a hydrocarbonoxy group, and R' includes an aliphatic unsaturated group) is used. A silane compound represented by a monovalent hydrocarbon group, a group Y, or hydrogen) and an organic peroxide that generates a free radical site may be added. Furthermore, the above-mentioned polyfunctional compound or silanolization condensation catalyst may be added. Examples of the silane compound include vinyltriethoxysilane, vinyltrimethoxysilane, T-methacryloxypropyltrimethoxysilane, and vinyl(β-methoxyethoxy)silane.

If necessary, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dioctoate, etc. are used as a silanolization condensation catalyst.

HMWPE is a crosslinking agent that crosslinks these polyethylenes.
The addition to the porous sheet can be carried out, for example, by sprinkling a crosslinking agent solution dissolved in an organic solvent onto the porous sheet of HMWPE, or by immersing the porous sheet of HMWPE in the crosslinking agent solution, and then drying and removing the organic solvent. This is done by At this time, the porosity of the HMWPE porous sheet is (2
), so the necessary amount of crosslinking agent is dissolved or dispersed in an amount of organic solvent that is sufficient to fill the voids, and this is HM
Sprinkle it on the WPE porous sheet or add H into it.
It is preferable to soak a porous sheet of MWPE, remove the excess solvent solution or dispersion adhering to the surface of the porous sheet between two round rods, and pull it up to dry it. Furthermore, P
A method may also be used in which a crosslinking agent is added to E powder particles, mixed with a V blender, Henschel mixer, etc., and then a porous sheet of HMWPE is formed.

Porosity - 1 - ((apparent density of porous sheet of HMWPE/(true density of HMWPE)) The crosslinking process is basically performed by heating in the peroxide crosslinking method, and in the silane crosslinking method. This refers to a process in which a silane compound is grafted onto polyethylene by heating.The silane crosslinking method requires a subsequent step of further carrying out a crosslinking reaction in the presence of moisture.

Xylene insoluble content (gel fraction, degree of crosslinking) indicating the degree of crosslinking
For the measurement, approximately 0.3 g of the sample was placed in a 200 mesh stainless steel wire mesh, and after extraction treatment in boiling xylene for 16 hours,
This is done by measuring the xylene insoluble content remaining on the stainless wire mesh.

A porous sheet of HMWPE containing a cross-linking agent is heated and pressed until the apparent density of the porous sheet is 8, which is the true density of HMWPE.
To eliminate porosity and simultaneously perform crosslinking treatment to seal HMWPE to 0% or more, it is possible to set the heating temperature to a temperature higher than the decomposition temperature of the organic peroxide and perform compression molding using a press or the like. . Generally, it is preferable to heat the organic peroxide at its half-life decomposition temperature, which is about three times longer than the half-life decomposition time.

In order to eliminate porosity by heating and pressing a porous sheet of HMWPE so that the apparent density of the porous sheet becomes 80% or more of the true density of HMWPE, the porous sheet is fused by heating and pressing to increase the density. This is done by increasing the As disclosed in JP-A-124842, porosity disappears when the apparent density of the porous sheet of HMWPE is H.
If the true density of MWPE is less than 80%, it is preferable that the sheet has a low ε1 and tan δ, but open cells remain in the HMWPE sheet and liquid may seep into the sheet during processes such as etching and through-hole plating. This is to improve the overall substrate characteristics since it has a negative effect on the substrate characteristics.

The heating and pressing conditions for heating and pressing molding are a heating temperature of 130 to 25
0°C1 applied pressure 20-80 kg/c+fl (0,
2 to 7.8 MPa) and the application time is preferably 2 to 10 minutes. In addition, it is preferable that the HMWPE porous sheet is sandwiched between stainless steel end plates or the like and heated and pressed under uniform conditions. At this time, crosslinking is completed at the same time, but in the case of the silane crosslinking method, the crosslinking reaction of the silane compound grafted product in the sheet obtained by heating and pressure molding is carried out in the presence of moisture to complete the crosslinking. This crosslinking condition is 20~
Preferably, the temperature is 80°C.

The HMWPE sheet, which has lost porosity above a certain value and is crosslinked, is heat treated at a temperature of 260°C or higher, preferably 260-300°C. The purpose of the heat treatment is to expose the HMWPE sheet to a heated atmosphere to remove inherent internal stress, decomposition residues of the crosslinking agent, and unreacted substances.

The maximum temperature applied to the board is the soldering temperature for connecting components, which is usually 260°C. Therefore, the heating atmosphere temperature should be 260°C or higher and the heat treatment time should be
5 to raise the temperature of the E-sheet to the heating atmosphere temperature and soften it.
Since it takes at least 5 seconds, it is preferable to use at least 5 seconds to relieve internal stress and remove decomposition residues of the crosslinking agent and unreacted substances. At this temperature, volatile components are removed in a very short time. PE is 2
Since oxidative deterioration begins at temperatures above 00°C, it is preferable to perform gas heating in an oxygen-free atmosphere, for example in an oven purged with a gas such as nitrogen, or in a heating medium such as silicone oil, molten salt, or molten metal. However, since a slight oxidation of HMWPE is preferable for increasing the adhesion with the adhesive layer or resin-impregnated reinforcing layer, some oxidation of the surface layer is acceptable.

HMWPE is used for cooling after heat treatment to relieve internal stress.
To make a sheet free without fixing it so that no stress is applied to the sheet. For example, in the hatch method, cooling may be carried out by placing the material on a patch plate, or in the continuous method, cooling may be performed using roller conhairs with narrow intervals. The upper limit of heat treatment temperature is PE decomposition temperature, ignition, and ignition temperature of approximately 330°C.
Because of the above, it is preferable to perform the treatment at a temperature below this temperature. Particularly preferred is 260 to 300°C.

Then, HMWPE was heat treated at a temperature of 260°C or higher.
A high-frequency substrate is obtained by laminating a metal foil or a metal plate on the base via a sheet, an adhesive layer, or a resin-impregnated reinforcing layer.

Examples of metal foils and metal plates to be laminated include gold, silver, copper, aluminum, nickel, stainless steel, iron, iron alloy, copper alloy, and the like. Preferred are copper foil, aluminum foil, aluminum plate, and iron alloy plate. The thickness of the metal foil or metal plate is preferably 10 to 50 μm.

The adhesive layer is for strengthening glabellar adhesion in a high frequency substrate such as a HMWPE sheet, metal foil or metal plate.

If the structure of the adhesive layer contains many polar groups, the dielectric's ε1 and t
anδ may become high.

In such cases, it is desirable to minimize the thickness of the adhesive layer.

Adhesives, adhesive films, etc. are used as the adhesive layer, and examples of adhesives include acrylic resin, polyester resin, polyurethane resin, phenol resin, epoxy resin, chloroprene rubber, nitrile rubber, epoxy phenol, butyral phenol, and nitrile phenol. etc. In addition, as adhesive films, (1) ethylene-vinyl acetate copolymer, ethylene-acrylic ester copolymer, ethylene-acrylic acid copolymer, ethylene-maleic acid copolymer, ethylene-maleic anhydride grafted α,β-unsaturated carboxylic acid,
A copolymer obtained by conventional copolymerization or graft copolymerization of its ester, anhydride, or metal salt thereof, or a saturated organic carboxylic acid, (It) a mixture of a polyolefin and the copolymer of (I), ( An example is a film of an adhesive composition in which a tackifying side, etc. is blended into a polyolefin.The adhesive layer has a crosslinkable group in its composition, and is free from ionizing radiation, organic peroxides, silane compounds, etc. Preferably, those that are crosslinked by

Furthermore, it is preferable to laminate a resin-impregnated reinforcing layer and a metal foil or metal plate on the HMWPE sheet directly or via an adhesive. The lamination molding conditions are the same as the heating and pressing conditions for the porous sheet.

As the resin-impregnated reinforcing layer, glass cloth, glass nonwoven fabric, plastic fiber woven fabric, etc., which are usually used for substrates, can be used.
A nonwoven fabric or other reinforcing agent impregnated with a curable resin face and dried is used.

Examples of resins include polyester resin, epoxy resin, phenol resin, melamine resin, diallyl phthalate resin,
Polyimide resin, bismaleimide/triazine resin, P
Examples include resin compositions of PO resins or PPS resins and crosslinkable polymers or crosslinkable monomers, and preferably polyester resins, epoxy resins, and polyimide resins with relatively low ε and tan δ are used.

[Effect]

The factors that increase tan δ are decomposition residues and unreacted substances of the crosslinking agent used when crosslinking PE, and in order to remove these, the crosslinked PE sheet can be scattered and removed in a high temperature atmosphere, but the molecular weight Using normal PE with a value of 50,000 to 200,000,
When this was cross-linked to form a PE sheet and heat treated on a flat plate coated with fine inorganic powder to cause free deformation at a temperature of 260°C or higher, the cross-linked PE sheet was transparent, exhibited rubber elasticity, and showed no distortion. It retains its shape even when it is deformed and becomes uneven in thickness and cooled. If metal foil is laminated on this via an adhesive, distorted deformation can be corrected to some extent, but thickness unevenness and deformation will result in poor appearance and thickness accuracy that can be discerned through the metal foil.

On the other hand, the HMWPE sheet obtained by crosslinking the HMWPE porous sheet at the same time as the porosity disappears has a 260%
Although dimensional changes (shrinkage) occurred even when heat-treated at a temperature higher than °C, no distorted deformation or thickness unevenness occurred.

This difference seems to be due to the method used to mold the crosslinked PE. In the case of normal PE with a molecular weight of 50,000 to 200,000,
Cross-linked PE sheets created by peroxide cross-linking are mixed with PE in an extruder at a temperature that does not decompose the organic peroxide, and then pelletized or formed into a sheet with a T-die, or a T-die is formed near the tip of the extruder.
A method of directly molding a crosslinked PE sheet by decomposing the organic oxide using a die. The pellets are further compression-molded using a press or the like to form the pellets into a sheet and cross-linked at the same time, or the pellets are first formed into a PE sheet and then further heated and pressed to form a cross-linked PE sheet. In this series of steps,
When a crosslinked PE sheet is formed by mixing an organic peroxide with PE, the PE must be fluidized, and at this time internal stress is inherent in the crosslinked PE sheet. In particular, when a crosslinked PE sheet is molded under heat and pressure at a temperature higher than the decomposition temperature of the organic peroxide, internal stress is likely to occur because the crosslinked PE that has become highly viscous is fluidized.

In the case of HMWPE porous sheets, there is almost no flow in the plane direction of the PE sheet, and the thickness decreases only in the thickness direction.
The powder particles that make up the sintered porous sheet act to fill the porous voids, and the PE in the PE powder particles used is fused, sorted, and crosslinked with almost no flow, reducing internal stress. becomes lower. Therefore, the sheet will not be significantly deformed during heat treatment at a high temperature of 260° C. or higher, which has not been used in the past, and no thickness unevenness will occur. At this temperature, decomposition residues of the crosslinking agent and unreacted substances are scattered and removed in a short time, so that the value of tan δ becomes extremely low.

Heat treatment at temperatures below 260°C requires a long time for the decomposition residue of the crosslinking agent and unreacted substances to scatter, and long-term treatment may cause deterioration of the PE or staining of the heat treatment medium and the surface of the PE, such as solder, etc. When using heat media such as molten metal salt or silicone oil, a large amount of them adheres to the surface of PE, making the separation work complicated. Furthermore, in order to improve the dimensional stability of the substrate because the internal stress relaxation of the crosslinked PE sheet is not sufficient, it is necessary to increase the proportion of the resin-impregnated reinforcing layer, which is made by impregnating a glass cloth with good dimensional stability with an epoxy resin, for example. As a result, ε and tan δ increase.

Further, when this substrate is used for circuit processing and used as a printed wiring board, decomposition residues of the crosslinking agent and unreacted substances gradually scatter and the dielectric properties change, making it undesirable.

〔Example〕

Example 1 Using the apparatus shown in FIG. 1, a polyester film (SL type, Teijin Ltd.) base material 1 with a thickness of 50 μm was placed along a stainless steel belt 2, and coated with a hand-nose coater 3.
MWPE powder 4 (Miperon XM220, average particle size 0.
03mm, melting point 136°C1, bulk density 0.4g/d, true density of polyethylene 0.94g/cr1, Mitsui Petrochemical Industries Co., Ltd. trade name) was formed to a thickness of 0.8 mm on the base material 1. The mixture was heated and sintered in a heating furnace (160° C.) to obtain a porous sheet of HMWPE with an apparent density of 0.5 g/1 liter of Cl.

Using organic peroxide t-butylcumyl peroxide as a crosslinking agent, the amount of organic peroxide calculated to fill the voids in the porous sheet is 0.6 parts by weight per 100 parts by weight of the porous sheet. of toluene, sprinkle this solution uniformly on a porous sheet, air dry it, and then heat it at 100°C.
It was dried in a dryer for 5 minutes. Two of these porous sheets were stacked and sandwiched between stainless steel mirror plates with a 50 μm thick polyimide film for mold release in between.
Heated and pressurized for 5 minutes under pressing conditions of kg/cd (2.0 NPa), and the porosity disappeared, thickness 0.85 m, density 0°9
A peroxide crosslinked sheet of HMWPE with a weight of 3 g/cd was obtained.

The xylene insoluble content of this sheet was 38% by weight. This peroxide cross-linked sheet was further sandwiched between the stainless steel end plates mentioned above and was heated to 300°C in a press to give a weight of 40kC.
/cd (3.9 MPa), after heating and pressurizing for 2 minutes, releasing the pressure for 15 seconds, and after heating and pressuring for another 1 minute, releasing the pressure,
The stainless steel end plate was transferred to a separate cooling-only press and brought into contact with the press surface without applying pressure to cool it to room temperature and perform heat treatment.

Next, on both sides of this HMWPE sheet, an adhesive layer of 10
50 μm attomer N irradiated with Mr a d electron beam
A film of EO60 (trade name of Mitsui Petrochemical Industries, Ltd., linear low-density polyethylene grafted product) (xylene insoluble content, 70% by weight) was provided, and an electrolytic copper foil with a thickness of 35 μm was applied to one side via this adhesive layer. , thickness IIIll on the other side
Laminated aluminum plates of 200"C120kg/c
A high frequency substrate was obtained by heating and pressing under conditions of +11.

Comparative Example 1 Peroxide crosslinked HMWPE sorting in Example 1
A high frequency substrate was obtained in the same manner as in Example 1 except that the heat treatment at 0°C was not performed.

Example 2 0.2 parts by weight of 25-dimethyl-2,5-di(t-butylperoxy)hexyne-3 was added as an organic peroxide to 100 parts by weight of the HMWPE porous sheet obtained in Example 1. 1 part by weight of vinyltriethoxysilane as a silane compound and 0.05 part by weight of dibutyltin dilaurate as a silanolization condensation catalyst were dissolved in toluene in an amount calculated to fill the voids in the porous sheet. Sprinkle this evenly on the porous sort, and after air-dry it at 100°C.
It was dried in a dryer for 5 minutes. Two of these porous sheets were stacked and sandwiched between stainless steel end plates with a 50 μm thick polyimide film for mold release in between, and a 200"C140kg
/cffl (3.9MPa) for 5 minutes under heat and pressure to create a dielectric with a thickness of 0.85mm and porosity disappearing.
．． A run-crosslinked sheet of HMWPE with a weight of 93 g/c+Il was obtained. Next, place this notebook in warm water at 80°C for 3 minutes.
It was immersed for an hour to crosslink, and then dried in a dryer at 95°C for 1 hour to obtain a silane crosslinked HMWPE sheet.

The xylene insoluble content of this sheet was 62% by weight. After immersing this silane crosslinked HMWPE sheet in a silicone oil bath heated to 270°C for 10 seconds (heat treatment),
The silicone oil adhering to the sheet surface was removed by washing it several times in toluene and drying it at 115°C for 5 minutes. Next, on both sides of this HMWPE sheet, 10 Mr.
50 μm attomer NEO6 irradiated with electron beams a and d
A film with a thickness of 3 is provided on one side through this adhesive layer.
A 5 μm electrolytic copper foil was laminated on the other side with an aluminum plate 1 cm thick, 200°C, 20 kg/cd (2,0 MP
A high frequency substrate was obtained by heating and pressing under the conditions of a).

Comparative Example 2 In Example 2, the silane crosslinked HMWPE sheet was
A high frequency substrate was obtained in the same manner as in Example 2, except that the substrate was not immersed in a silicone oil bath heated to .degree.

Example 3 A peroxide crosslinked sheet obtained in the same manner as in Example 1 was
After being immersed in a silicone oil bath heated to 115° C. for 10 seconds (heat treatment), the silicone oil adhering to the sheet surface was washed several times in toluene and was removed by drying at 115° C. for 5 minutes. Then, a glass cloth having a thickness of 60 μm was impregnated with the following formulation and dried to obtain a resin-impregnated reinforcing layer. The compound is polyphenylene oxide: 100 parts by weight of PPO534J (product name of Engineering Plastics Co., Ltd.);
Terminal acryloyl group-modified 1,4-polybutadiene: R
-45ACR (Product name of Idemitsu Petrochemical Co., Ltd.) 40fi
parts by weight, 20 parts by weight of triallylisocyanurate and 25 parts by weight of perhexine B: 2°5-dimethyl-2,5-di(
Dissolve 2 parts by weight of t-butylperoxy)hexyne-3 (trade name of NOF Corporation) in toluene and add 2 parts by weight of toluene.
It was used as a 0% by weight solution.

Copper foil with a thickness of 35 μm is laminated on both sides of the peroxide-crosslinked heat-treated sheet via the resin-impregnated reinforcing layer,
1 at 220°C and 140kg/d (3.9MPa)
The mixture was heated and pressed for 5 minutes to obtain a high frequency substrate with a dielectric thickness of 1°08 m+.

Comparative Example 3 A high frequency substrate was obtained in the same manner as in Example 3 except that the peroxide crosslinked HMWPE sheet was not heat treated.

The ε1 and tan δ of the high frequency substrates obtained in Table 1 and above Examples 1 to 3 and Comparative Examples 1 to 3 were measured, and the results were summarized in Table 1.
Shown in the table. Further, the copper foil and aluminum plate of the high frequency substrate obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were etched with a ferric chloride hydrochloric acid solution, washed with water, and dried, and the resulting dielectric sheet was heated at 260°C. We measured the change in the thickness of the dielectric sheet when it was floated in a solder bath for 20 seconds, and the results also showed that
Shown in the table.

°1 Thickness change (%) × 100 Example 4.5 and Comparative Examples 4 to 6 Silane frame i) obtained in the same manner as Example 2 (using a MWPE sheet, varying the temperature of the silicone oil bath and the immersion time) Except for the above, a high frequency substrate was obtained in the same manner as in Example 2. This substrate was floated in a solder bath at 260° C. for 20 seconds, and the presence or absence of blisters was examined. The metal on the substrate was also etched away, and the results shown in Table 1 were obtained. Similarly, tan δ and thickness change were measured and the results are shown in Table 2.

The tan δ of the high frequency substrates obtained in Examples 1 to 5 is lower than that of the substrates obtained in Comparative Examples 1 to 6,
The effect of heat treatment is visible.

Furthermore, changes in thickness due to changes in dimensions of the dielectric of the high-frequency substrate are also significantly reduced. By reducing the value of tan δ to about half, weak signals can be transmitted with less loss.

PE (Sumi Rikisen Fl) which is usually used as a reference
0.6 parts by weight of the organic peroxide used in Example 1 was kneaded with an extruder using an extruder, and then this was further sandwiched between stainless steel mirror plates. 200 through 0.85 cabinet spacer
Peroxide crosslinked PE sheet obtained by heating and pressurizing at 120 kg/cj (2, OMPa) for 5 minutes (xylene insoluble content: 6
5% by weight) in a silicone bath heated to 270°C.
I tried dipping it for a second, but when I pulled the sheet out of the silicone bath, the part that was holding the sheet stretched and deformed, making the thickness uneven.

On the other hand, the HMWPE sheet did not stretch or deform.

〔Effect of the invention〕

By heat-treating the cross-linked HMWPE sheet at a high temperature of 260°C or higher, which has not been used conventionally, as in the present invention, decomposition residues of the cross-linking agent and unreacted substances can be removed.
The value of an δ can be significantly reduced. Furthermore, since internal stress is relaxed, dimensional changes in solder and the like when exposed to high temperatures are significantly reduced, and since the volatile content is reduced, blistering does not occur.

In a high-frequency board using an HMWPE sheet that is not heat-treated (not according to the present invention), after circuit molding, decomposition residues of the crosslinking agent and unreacted substances scatter over time, and as a result, the dielectric properties change over time, causing circuit impedance etc. This is not preferable because the design parameters change. In the present invention, this problem does not occur and the present invention is suitable.

In addition, by laminating a resin-impregnated reinforcing layer obtained by impregnating a reinforcing layer such as glass cloth with resin, it is possible to improve the warpage, strength, and surface hardness of the board, and it is also possible to isolate it from the outside air through this layer. can prevent oxidation of PE in high-temperature atmospheres such as soldering, and reduce ε, and ta due to oxidation.
It is possible to suppress the value of nδ from increasing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram of an apparatus for continuously forming a porous sheet of ultra-high molecular weight polyethylene (HMWPE). Explanation of symbols I material 2 Stainless steel belt hand-nose type coater Ultra-high molecular weight polyethylene powder heating furnace Diagram

Claims (1)

[Claims] 1. A porous sheet of ultra-high molecular weight polyethylene containing a cross-linking agent is heated and pressure-molded to eliminate the porosity and at the same time undergo cross-linking treatment so that the apparent density of the porous sheet becomes 80% or more of the true density of the ultra-high molecular weight polyethylene. After heat-treating the crosslinked ultra-high molecular weight polyethylene sheet obtained by performing this process at a temperature of 260°C or higher, metal foil or metal plate is laminated on both sides or one side of this sheet directly or via an adhesive layer or a resin-impregnated reinforcing layer. A method of manufacturing a high frequency substrate, characterized in that: