JPS61196594A - Electronic component mounting structure - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a mounting structure for electronic components, and more particularly to a mounting structure for electronic components mounted on a printed circuit board.

[Prior Art] For example, electronic devices such as electronic desktop calculators employ a structure in which electronic components such as ICs and LSIs are connected to a printed circuit board on which a wiring pattern is formed by etching or printing.

A flexible plastic sheet or a hard paper phenol board is used as the printed circuit board.

In such a mounting structure, electronic components, especially LSIs, can be connected and fixed by bonding them using solder, or by bonding them using solder.
It used a method of pressure welding using mechanical parts.

However, if such soldering or pressure welding methods are used,
Both methods require a large number of assembly steps, which increases costs and reduces productivity.

To solve this problem, a low melting point conductive adhesive is printed on the pattern of the printed circuit board to be connected, the lead terminals of LSI etc. are placed on top of that, and then an insulating adhesive is applied. A widely used method is to cover the connections with a flexible laminate sheet and then bond them by heating.

Although this method is low cost and suitable for mass production, it has the disadvantages that the bonding strength is insufficient, it is easy to peel off, and the contact resistance increases due to changes over time.

A conventional mounting structure for electronic components using this type of laminate sheet is shown in FIGS. 1 to 3. FIG. 1 shows an LSI as an example of an electronic component.

This LSII is illustrated as having 44 terminals, and in the illustrated example, 11 terminals protrude from each side of the quadrilateral LSI body.

Fig. 2 is a cross-sectional view of the connected state, and the reference numeral 3 in Fig. 1 is a printed circuit board made of polyester (polyethylene terephthalate), etc., and a conductive pattern 4 printed with conductive ink is formed on its top surface. There is.

The terminals 2 of the LSII are then fixed onto the conductive pattern 4 via the conductive adhesive 5.

This conductive adhesive 5 is commonly called hot melt, and conductive particles made of carbon or silver powder are combined with a thermoplastic resin binder such as synthetic rubber or polyamide resin and a solvent such as isophorone or seapentene. This mixture is applied onto the conductive pattern 4 by a printing method.

Of course, it is not applied to parts that do not require connection.

The terminal 2 of LIll is placed on the conductive adhesive 5, and the laminate sheet 6 is placed on top of the conductive adhesive 5, and the bonded portion is heated to, for example, Zoo-180° C. and pressurized to perform bonding.

The laminate sheet 6 is a reinforcing sheet formed as a flexible sheet from an insulating material such as polyester and coated with an insulating adhesive on the back surface.

In the illustrated example, a reinforcing polyester sheet is layered on top of the joint, which greatly increases the joint strength, unlike a structure that is fixed using only conductive adhesive. can be increased.

However, even if a laminate sheet is used to increase the bonding strength, the heat shrinkage rates of the printed circuit board material and the conductive adhesive are different, so stress concentrates on the terminal joints, causing the printed circuit board to warp or become uneven. This causes peeling of the terminals and a decrease in bonding strength, resulting in a significant increase in contact resistance.

[Purpose] The present invention has been made in order to eliminate the above-mentioned drawbacks of the conventional electronic components.It is an object of the present invention to provide a mounting structure for electronic components that has excellent bonding strength, requires few assembly steps, is low cost, and is suitable for mass production. The purpose is

[Summary of the Invention] In order to achieve the above object, in the present invention, electronic components are attached by making slits in the printed circuit board at the connection parts of terminals, which are legs, to connect the printed circuit board and conductive adhesive. We adopted a structure that diffuses the stress caused by the difference in thermal contraction rate between the two and suppresses an increase in contact resistance.

[Example] Hereinafter, the present invention will be described in detail based on the example shown in the drawings.

4 and 5 illustrate one embodiment of the present invention, and the same parts in the figures as in FIGS. 1 to 3 are given the same reference numerals, and the explanation thereof will be omitted.

In this embodiment, slits 7 are formed on the printed circuit board 3 side on both sides of the joint between the conductive pattern 4 and the terminal 2.

The length of this slit 7 is equal to or greater than the length of the joint portion of the terminal 2.

If the terminal 2 is bonded with such a slit formed and reinforced with the laminate sheet 6, even if stress occurs due to the difference in thermal shrinkage rate between the printed circuit board material and the conductive adhesive material, the slit area will remain intact. This allows the stress to be diffused so as not to cause stress concentration.

Therefore, an increase in contact resistance due to peeling or insufficient bonding strength can be prevented.

In addition, since stress concentration at the joint can be prevented, warping and unevenness of the printed circuit board can be prevented.
It is possible to maintain a high bonding strength.

[Effect] As is clear from the above description, according to the present invention, in an electronic component mounting structure in which a terminal of an electronic component is fixed to a printed circuit board side via a conductive adhesive, an insulating material is attached to the upper side of the terminal. The laminate sheet is fixed using an insulating adhesive, and a slit is formed on the printed circuit board side to sandwich the terminal joint, which reduces the heat shrinkage rate of the printed circuit board and conductive adhesive. Stress concentration due to the difference can be prevented, and contact resistance can be prevented from peeling off at the joints of the terminals or from increasing contact resistance due to insufficient joint strength.

[Brief explanation of the drawing]

Figures 1 to 3 explain the conventional structure. Figure 1 is a plan view, Figure 2 is a sectional view taken along line A-A in Figure 1, and Figure 3 is a cross-sectional view of Figure 1.
The enlarged sectional view taken along the line B-B in the figure, and FIGS. 4 and 5 are for explaining an embodiment of the present invention. FIG. 4 is a plan view, and FIG. It is a diagram. l... LSI 2... Terminal 3... Printed circuit board 4... Conductive pattern 5... Conductive It
i Adhesive 6... Laminate sheet 7... Slit Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] In an electronic component mounting structure, a conductive adhesive is applied to a conductive pattern on a printed circuit board, the connection terminals of electronic components are layered on top of the conductive adhesive, and the terminals are covered with a laminate sheet coated with adhesive. An electronic component mounting structure characterized by having slits formed in the printed circuit board on both sides of the part.