TABLE OF CONTENTS A solder joint must be designed to bring out its major advantages, as listed in the preface. These are listed in Table 4.1. The first three properties depend on both the material and the geometrical design. Mechanical durability (strength) also depends to a large extent on the process used and the alloy makeup. This has become especially important as we get into the use of lead-free solders in the twenty-first century. With the introduction of these new alloys, the design will become critical, because we lack a reliability database such as has been developed over time for the lead-base alloys.
| Design parameters | Material properties | Physical dimensions | Mechanical design |
|---|---|---|---|
| Electrical conductivity | Yes | Yes | No |
| Mechanical durability | Yes | Yes | No |
| Heat dissipation | Yes | Yes | No |
| Ease of manufacture | No | No | Yes |
| Simplicity of repair | No | No | Yes |
| Visual/instrument inspectability | No | No | Yes |
We have already seen that solder interacts with the base metals it wets, thus changing the metallurgical system. Here, time and temperature of soldering are critical factors depending on the process. Durability of the solder alloy, on the other hand, depends on its ability to act as a stress coupler. Excessive alloying and intermetallic crystal formation detract, in most cases, from the ductility of the solder and may shorten its long-term reliability. Thus, as the second design parameter listed in Table 4.1, we refer to mechanical durability rather than mechanical strength.
The first part of this chapter...
