TABLE OF CONTENTS The implementation of lead-free soldering is not a smooth ride. Challenges surface one by one in all aspects, including surface finishes, soldering processes, and reliability. In general, most of the challenges can be answered with certain approaches, although some of those approaches remain hypothetical or theoretical. However, some challenges still remain unanswered. In this chapter, most of the challenges encountered in lead-free soldering are listed and discussed.
SnPb plating and hot-air solder leveling (HASL) have been used by the electronics industry for decades. Although technical challenges still exist, in general most of the bugs have been worked out, and applications and usages of SnPb surface finishes are regarded as a routine operation with the major emphasis on maintaining control. The same cannot be said for lead-free surface finishes. Due either to the specific chemistry utilized or to the short history of these finishes, virtually every lead-free surface finish exhibits some challenges. In this section, several of these challenges are listed and discussed.
Electroless nickel/immersion gold (ENIG) is one of the prevailing lead-free surface finishes. It has been used by the industry for years due to its excellent solderability for fine-pitch surface-mount technology and ball grid array (BGA) package devices. This is particularly true for thick boards, where the electroplating process experiences difficulty in providing even plating for through-holes. However, sporadic solder joint failure may occur due to joint weakness. A number of investigations have been conducted.1 6 Puttlitz1 first reported a...
