JPH04186797A - Manufacture of multi-layer circuit board - Google Patents

Abstract

PURPOSE:To suppress bending by a method wherein, after a plurality of circuit boards is pressure-bonded, it is heat-treated under the crystalline melting point of crystalline thermoplastic resin and over the glass-transition temperature. CONSTITUTION:The insulation layer constituting a multi-layer circuit board is made of crystalline thermoplastic resin. The crystalline thermoplastic resin is a thermoplastic resin whose crystallinity can be more than 20% by sufficient heat-treatment. For example, polyarylenesulfide, polyarylenesulfidecaine, or polymer-blend which consists of more than two kinds of those reins can be given. A mitigation heat treatment is performed preferably over the crystallization temperature and under melting point, and more preferably, within the temperature range over the temperature in the process where parts are soldered the multi-layer circuit board in the post-processing and the melting point.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a multilayer circuit board using a thermoplastic resin as an insulating layer.

[Conventional technology] A multilayer circuit board is created by laminating multiple circuit boards with thermoplastic resin as an insulating layer and a circuit on one side, and after exposing the board to a high temperature atmosphere and soldering the components, the circuit board is heated to room temperature. Multilayer circuit boards may exhibit curvature depending on the type of resin and temperature.

[Problems to be Solved by the Invention] An object of the present invention is to provide a method for suppressing as much as possible the curvature that occurs when a multilayer circuit board is soldered in a high temperature atmosphere and returned to room temperature after being molded.

[Means for Solving the Problem] (Summary) The gist of the present invention is that after bonding a plurality of circuit boards made of an insulating layer and a conductor layer made of a crystalline thermoplastic resin under pressure, Hereinafter, the present invention will be described in detail, which is a method of manufacturing a multilayer circuit board characterized by performing relaxation heat treatment at a temperature below the crystal melting point and above the glass transition temperature.

(Multilayer circuit board lamination step) The insulating layer constituting the multilayer circuit board is made of crystalline thermoplastic resin. The insulating layer may contain substances other than the crystalline thermoplastic resin, and the crystalline thermoplastic resin may be used alone or in a composition of two or more types. In the case of a composition, one of the two may form a fibrous or dispersed phase.

In addition to the crystalline thermoplastic resin, there are no particular restrictions on what may be included, but inorganic fibers such as glass fibers and potassium titanate fibers, inorganic or organic additives such as mica, kaolin, and calcium stearate, etc. is exemplified.

The crystalline thermoplastic resin is not particularly limited, and known heat-resistant crystalline thermoplastic resins may be used. Here, heat resistance means having solder resistance, and means that the melting point of the crystalline thermoplastic resin is higher than the melting point of solder. Furthermore, the term "crystalline thermoplastic resin" means a thermoplastic resin whose crystallinity can be reduced to 20% or more by sufficient heat treatment, such as polyarylene sulfide, polyarylene sulfide ketone, polyether ether ketone, polyether ketone, or any of these. Examples include polymer blends consisting of two or more types of resins. Here, the degree of crystallinity (Xc) is determined from the following equation after separately determining the amorphous density ρ, which is lower than the density value (ρ) determined by the density gradient tube.

xc-(ρ./ρ) ((ρ-ρ,)/(ρ.-ρ,))
The crystal density ρ is determined separately. For the closure, a value determined by calculation after determining the lattice constant by X-ray diffraction is used, and for the amorphous density ρ, an actually measured value is used. For example, the crystal density of polyphenylene sulfide is 1.430 g/cm3, and the amorphous density is 1.313 g/cm3.

A known molding method is employed as a manufacturing method for obtaining such an insulating layer, but whichever molding method is used, it is desirable to perform a tension heat treatment and then a relaxation heat treatment before lamination.

On the other hand, examples of the conductor constituting the conductor layer of the multilayer board include a conductive resin composition using the same or similar thermoplastic resin as the binder to the thermoplastic resin constituting the insulating layer, metal, etc., and the conductor layer is also known. in a way.

Obtainable.

In addition, multilayer circuit boards are bonded with adhesive by heating under pressure.
Or they can be laminated without intervening. When no adhesive is used, lamination can be achieved by applying pressure at a temperature close to the melting point of the thermoplastic resin, usually within ±10° C. of the crystal melting point, and holding it for a period of time long enough to prevent it from flowing.

(Relaxation heat treatment step) In the present invention, relaxation heat treatment is performed at a temperature below the crystal melting point and above the glass transition temperature of the crystalline thermoplastic resin constituting the multilayer circuit board as described in 2.

The relaxing heat treatment is preferably carried out at a temperature that is higher than the crystallization temperature and lower than the melting point, more preferably higher than the temperature of the subsequent step of soldering and fixing the component on the multilayer circuit board, but lower than the melting point. Here, the glass transition temperature, crystal melting point, and crystallization temperature are measured using a differential scanning calorimeter, and are
Endothermic peak 1 when transitioning to a rubber state that appears when an amorphous pellet thermoplastic resin is heated at a rate of °C/min;
Refers to the endothermic peak during melting and the exothermic beep that appears in between.

However, when a resin composition has two or more glass transition temperatures, crystal melting points, and crystallization temperatures, the main peaks thereof are defined as the glass transition temperature, crystal melting point, and crystallization temperature, respectively.

The relaxation heat treatment referred to in the present invention may be heat treatment under processing conditions such that strain generated during the lamination process is relaxed, and stress may be applied to some extent. For example, stress may be applied as if a plurality of circuit boards were stacked on top of each other without being bonded to each other. However, heat treatment under tension, such as fixing both ends, is inappropriate.

Such relaxing heat treatment may be performed after lamination and adhesion and cooling, or may be performed during the cooling process after lamination and adhesion. The time required for the relaxation heat treatment is longer as the temperature of the relaxation heat treatment is closer to the glass transition temperature, and it also depends on the degree of strain applied during lamination.

[Example] (Measurement method) Heat shrinkage rate: A multilayer circuit board was cut into 100 mm in length and width, and a cross with a length of about LOO mm was stamped parallel and perpendicular to the extrusion direction.
It was placed on a flat surface, a transparent acrylic plate was placed on it, and its length was measured from above using a microscope. Next, the acrylic board was removed, the multilayer circuit board was placed on copy paper, and placed in a hot air oven at a predetermined temperature for 10 minutes. Then, after being left to stand at room temperature, the length was measured using a microscope in the same manner as before measurement. This operation was repeated three times and the heat shrinkage rate was determined from the average value.

(Comparative example) Silver paste was applied to one side of each of three commercially available polyphenylene sulfide films, and after drying at 150°C,
Heat 5 molecules at 3℃ and increase the initial pressure to 10kg/cm2 at that temperature.
Then, press lamination was performed for 4 minutes. Then, it was slowly cooled down to below the glass transition temperature over 3 hours. IC on this multilayer circuit board
etc. were soldered at 230°C and cooled. The heat shrinkage rate was 0-6% in the extrusion direction of the thermoplastic resin and 0.8% in the direction perpendicular to the extrusion direction, and a considerable degree of curvature was observed.

(Example) The multilayer circuit board of Comparative Example before soldering was subjected to relaxation heat treatment at 230° C. for 10 minutes, and then IC etc. were soldered at 230° C. and cooled. The heat shrinkage rate was 0.1% or less in the extrusion direction of the thermoplastic resin and 0.1% or less in the direction perpendicular to the extrusion direction, and the curvature was also suppressed to an almost unnoticeable level.

[Effects of the present invention] According to the present invention, the multilayer circuit board can be heat-shrinked compared to the conventional one.
The ratio became almost negligible, making it possible to suppress the curvature.

Claims (1)

[Claims] (1) After bonding a plurality of circuit boards made of an insulating layer and a conductor layer made of a crystalline thermoplastic resin under pressure, a relaxation heat treatment is performed at a temperature below the crystal melting point and above the glass transition temperature of the crystalline thermoplastic resin. A method for manufacturing a multilayer circuit board