JP3365405B2 - Electronic component mounting method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a method of mounting an electronic component in which a bump of the electronic component is fixed to an electrode of a printed circuit board. 2. Description of the Related Art As an electronic component, there is known an electronic component in which a molded body for sealing a chip with a resin is formed on an upper surface of a substrate and a bump is formed on a lower surface of the substrate. Such electronic components are mounted with the bumps aligned with the electrodes of the circuit pattern of the printed circuit board, and the printed circuit board is sent to a heating furnace, heated in the heating furnace to melt the bumps, and then cooled and solidified. Thereby, the bumps are fixed to the electrodes of the printed circuit board. Hereinafter, a conventional method for mounting electronic components will be described. FIG. 6A is a front view of an electronic component mounted on a conventional printed circuit board before bump fixing, and FIG. 6B is a front view of the electronic component after conventional bump fixing. FIG. 6 (a)
1, 1 is an electronic component, 2 is a substrate, 3 is a molded body made of a synthetic resin, 4 is a bump, 5 is a printed board, and 6 is an electrode of a circuit pattern of the printed board 5. As shown in the figure, the electronic component 1 is likely to be warped a. The warpage a is mainly caused by the curing shrinkage of the mold body 3 that occurs when the mold body 3 is formed. [0006] As shown in FIG. 6 (a), after the electronic component 1 is mounted on a printed circuit board 5,
Is sent to a heating furnace and heated. Then, the bumps 4 are melted and then cooled, and the bumps 4 are solidified and fixed to the electrodes 6. FIG. 6B shows a state after the fixing. However, in the above-mentioned conventional method, if the warpage a of the electronic component 1 is large, the bumps 4 at both ends cannot be grounded and fixed to the electrode 6 as shown in FIG.
It was defective. SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of mounting an electronic component that can securely fix all the bumps to electrodes of a printed circuit board even if the electronic component has a large warp. SUMMARY OF THE INVENTION Accordingly, the present invention provides a method for mounting a warped electronic component on a printed circuit board and heating the same to melt the bumps and correct the warpage by the heating. Then, all the melted bumps are adhered to the electrodes of the printed circuit board and then cooled to solidify the bumps. According to the above configuration, even if the electronic component has a large warp, all the bumps can be securely fixed to the electrode by heating to a temperature at which the warp is almost corrected. Next, an embodiment of the present invention will be described with reference to the drawings. FIGS. 1A, 1B, and 1C are explanatory views of a mounting process of an electronic component according to an embodiment of the present invention. 1A is a front view of an electronic component mounted on a printed circuit board before the bumps are fixed, FIG. 1B is a front view of the bumps being heated and melted, and FIG. 1C is a view after the bumps are fixed. It is a front view. In the figure, 1 is an electronic component, 2 is a substrate, 3 is a molded body made of a synthetic resin, 4 is a bump, 5 is a printed board, and 6 is an electrode. As shown, the electronic component 1
Is liable to cause warpage a. The warpage a is caused by a difference in the coefficient of thermal expansion between the substrate 2 and the mold body 3. As shown in FIG. 1A, after the electronic component 1 is mounted on a printed board 5,
Is sent to a heating furnace and is heated to a temperature (230 ° C.) or higher, which will be described later. Then, as shown in FIG. 1B, the warp a of the electronic component 1 is corrected, and all the bumps 4 that have been heated and melted adhere to the electrodes 6 of the printed circuit board 5. Then, when cooled, the bumps 4 are solidified and fixed to the electrodes 6 (FIG. 1C). According to this method, the warpage a of the electronic component 1 is corrected during heating in the heating furnace, and all the bumps 4 are fixed to the electrodes 6. The reason and method will be described below. FIG. 2 is a diagram showing the relationship between the temperature and the elongation of the material in one embodiment of the present invention. FIG. 3 is a diagram showing the correlation between the degree of warpage of the electronic component and the heating temperature in one embodiment of the present invention. Is a correlation diagram of the warpage of the electronic component and the bonding failure rate of the bump and the electrode in one embodiment of the present invention,
FIG. 5 is a temperature profile diagram in the heating furnace according to one embodiment of the present invention. In FIG. 2, there is a difference in the coefficient of thermal expansion between the substrate 2 and the mold body 3, and when the temperature of the substrate 2 and the mold body 3 exceeds a certain temperature (glass transition points a and b), the elongation increases sharply. For example, when the material of the substrate 2 is glass epoxy, the glass transition point a is about 140 ° C., and when the material of the mold body 3 is epoxy resin, the glass transition point b is about 120 to 140 ° C. In FIG. 3, the warpage a of the electronic component 1 decreases as the heating temperature increases, and at 230 ° C., the warp decreases to 50 μm. This is because, as the heating temperature increases, the elongation of the mold body 3 becomes larger than the elongation of the substrate 2 as shown in FIG. 2 and the difference between the two increases, thereby offsetting the difference in shrinkage. is there. In FIG. 4, the height of the bump 4 is 60.
In the case of about 0 μm, when the warpage is 80 μm or less, the bonding failure rate becomes zero. That is, from FIGS. 3 and 4, it can be seen that if the electronic component 1 is heated to 230 ° C. or more to reduce the warpage to 80 μm or less, the bonding failure rate becomes 0 and all the bumps 4 are fixed to the electrodes 6. Therefore, when heating the electronic component 1 in a heating furnace, as shown in FIG.
The warp is corrected, and all the bumps 4 adhere to the electrodes 6 of the printed circuit board 5 as shown in FIG. 1B, and then are fixed to the electrodes 6 when cooled as shown in FIG. 1C. The bump 4 is made of a solder material, and its melting temperature is
As shown in FIG. In FIG. 5, the temperature profile indicated by the dashed line is the case of the above-described conventional example. Since the heating is performed only to 230 ° C. or less, the warpage of the electronic component 1 is not corrected to 50 μm or less, and defective products are generated. It is a thing. As described above, according to the present invention, even if the electronic component has a large warp, the warp is corrected during heating, and all the bumps are securely fixed to the electrodes of the printed circuit board. it can.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A is an explanatory diagram of an electronic component mounting process according to an embodiment of the present invention. FIG. 1B is an explanatory diagram of an electronic component mounting process according to an embodiment of the present invention. c) An explanatory view of a mounting process of an electronic component according to an embodiment of the present invention. FIG. 2 is a diagram showing a correlation between temperature and elongation of a material according to an embodiment of the present invention. FIG. 4 is a diagram showing the correlation between the degree of warpage of the electronic component and the heating temperature in the embodiment. FIG. 6 (a) is a front view of an electronic component mounted on a conventional printed circuit board before fixing a bump, and FIG. 6 (b) is a front view of an electronic component mounted on a conventional printed circuit board after fixing the bump mounted on the conventional printed circuit board. Front view of electronic components 1) Electronic components 2 Substrate 3 Mold 4 Bump 5 Printed circuit board 6 Electrode

Continuation of the front page (56) References JP-A-5-275846 (JP, A) JP-A-60-111497 (JP, A) JP-A-2-134896 (JP, A) JP-A-6-224550 (JP) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H05K 3/34 H01L 21/60 H01L 23/12

Claims (1)

(57) [Claim 1] A synthetic resin mold for sealing a chip is formed on an upper surface of a substrate and a bump is formed on a lower surface of the substrate, and the synthetic resin mold is cured. An electronic component mounting method for mounting an electronic component having warpage due to shrinkage on a printed circuit board, wherein the electronic component is mounted on the printed circuit board and heated to melt the bumps and correct the warpage by the heating. Then, all the melted bumps are attached to the electrodes of the printed circuit board, and then the bumps are solidified by cooling.