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CHAPTER 4 NOTES ON MOUNTING
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When taking measures to prevent or correct mounting defects, it is important to understand the behavior of the solder joint when heat is applied during reflow processing. Figure 4-7 shows an example of the bonding process of a BGA device observed using a high-temperature observation device. In this example, when heat is applied (after preheating) and the temperature reaches melting point, the solder paste melts and the solder starts to coat the balls. When all the balls have melted, the device starts to subduct. In order to obtain a good bond, the device must subduct sufficiently. In this example, subduction is complete after about 20 seconds at melting point or higher. |
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Heat application conditions (temperature on underside of mounting board)
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Figure 4-7. Process in Which Good BGA Bond Is Obtained
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Examples of BGA mounting defects are shown below. 4.3.1 Case 1. Insufficient heat application 4.3.3 Case 3. Solder joint detachment (ball falloff) |
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