JP2001068821A - Technique for bonding heat sink to printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a halo from occurring around a reference hole by a method wherein a pair of an upper and a lower reference hole out of reference holes bored in two bonding plates are set larger in diameter than a stack pin. SOLUTION: A reference hole 6 is provided to bonding plates 1, a printed wiring board 3, a heat sink 4, and a no-flow prepreg 5 respectively, and a stack pin 2 is inserted into the reference holes 6 bored in them to fix. The four reference holes 6 are provided, and two reference holes 7 out of the reference holes provided to the bonding plates 1 are set larger in diameter than the stack pin 2. By this setup, a part of the stack pin 2 is not fixed to the bonding plates 1, so that stress imposed on the inner circumferential surface of the printed wiring board 3 in a bonding operation can be relaxed, and a halo can be prevented from occurring around a reference hole provided to the printed wiring board 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for bonding a heat sink to a printed wiring board.

[0002]

2. Description of the Related Art In order to bond a printed wiring board and a heat sink, a conventional no-flow type prepreg is processed into the shape of the heat sink, and the printed wiring board, the processed prepreg, The prepreg is overlapped in the order of the heat sinks, the stack pins are inserted into reference holes provided in each of the components, positioned and pinched, and the prepreg is softened by heating and pressing, and the resin of the prepreg is printed on the printed wiring board. This is completed by filling the gap between the heat sink and the heat sink and then curing.

[0003]

However, the printed wiring board (for example, made of glass cloth epoxy copper clad laminate), the heat sink (for example, made of aluminum plate), and the bonding plate (for example, made of stainless steel plate) have different coefficients of thermal expansion. For this reason, stress is applied to the reference hole into which the stack pin is inserted during heating and pressing. Due to the effect of this stress, harrowing around the reference hole of the printed wiring board (when a fine gap is formed between the glass fiber and the resin of the glass cloth epoxy resin that is the base material of the printed wiring board, white spots are observed from the surface Phenomenon). Since the reference hole uses a mounting hole or the like of a printed wiring board, if significant haloing occurs, the commercial value of the printed wiring board is lost. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a method of bonding a heat sink to a printed wiring board, which prevents occurrence of haloing around a reference hole.

[0004]

According to a first aspect of the present invention, a method of bonding a heat sink to a printed wiring board comprises the steps of: bonding the printed wiring board to a pair of bonding plates; In the step of positioning, pinching, and thermocompression bonding with the stack pins in the reference holes provided in the respective heat sinks in the order of the heat sinks, at least a pair of upper and lower reference holes out of the plurality of reference holes formed in the two bonding plates. The diameter is larger than the stack pin diameter.

According to the method of bonding a heat sink to a printed wiring board according to the first aspect, at least one of the stack pins inserted into the reference hole for fixing the printed wiring board and the heat sink is fixed to the bonding plate. Therefore, the printed wiring board and the heat sink can be released without being suppressed by the stack pins due to the difference in thermal expansion coefficient between the printed wiring board and the heat sink during heating and pressing.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of the present invention, and FIG. 2 is a perspective view showing a state of stacking (stacking). 1 and 2, 1 is a bonding plate, 2 is a stack pin, 3 is a printed wiring board, 4 is a heat sink, 5 is a no-flow prepreg, and the bonding plate 1, printed wiring board 3, heat sink 4, no-flow prepreg Reference holes 6 are provided in each of the reference numerals 5 and fixed by the stack pins 2. FIG. 2 shows an embodiment in which the number of reference holes 6 is four and the number of reference holes 7 of the bonding plate 1 out of the reference holes of the bonding plate 1 is larger than the diameter of the stack pin.

The printed wiring board 3 and the heat sink 4 expand and contract, respectively, at the stage of stacking and heating / pressing / cooling in the state of FIG. 1, but since the horizontal movement is suppressed by the stack pins 2, the stress is reduced in the reference hole. Hang on the circumference. However, since the two stack pins 2 ′ are not fixed to the bonding plate, the stack pins 2 ′ can move slightly according to the expansion and contraction of the printed wiring board 3 and the heat sink 4. Therefore, stress applied to the inner peripheral surface of the reference hole of the printed wiring board 3 and the heat sink 4 is reduced. In this embodiment, two pairs of reference holes of the bonding plate having a diameter larger than the stack pin diameter are provided, but the number of holes can be determined according to the shapes of the printed wiring board 3 and the heat sink 4. Although the printed wiring board, the no-flow prepreg, and the heat sink are stacked in this order between the pair of bonding plates, it is needless to say that the stacking order may be reversed.

[0008]

According to the present invention, since a part of the stack pins is not fixed to the bonding plate, the stress applied to the inner peripheral surface of the reference hole of the printed wiring board during the bonding operation is alleviated. Haloing can be prevented from occurring around the hole.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one embodiment of the present invention.

FIG. 2 is a perspective view showing a state of stacking according to one embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 1 bonding plate 2 stack pin 2 'stack pin not fixed to bonding plate 3 printed wiring board 4 heat sink 5 no-flow prepreg 6 reference hole 7 reference hole of bonding plate larger than stack pin diameter

Claims (1)

[Claims] At the time of bonding a printed wiring board and a heat sink, the printed wiring board, a shape-processed no-flow prepreg, and the heat sink are positioned by stack pins between the pair of bonding plates in the order of the reference holes. In the step of sandwiching and thermocompression bonding, a diameter of at least a pair of upper and lower reference holes of the plurality of reference holes formed in the two bonding plates is made larger than the stack pin diameter. Heat sink bonding method.