Solder attachment

After mechanical attachment to a substrate, a leadframe, or to the inside of a package, bare die or chip devices are electrically connected by one of five methods wire bonding, flip-chip bonding, TAB, solder attachment, or attachment with electrically conductive adhesives. Fig. 1.6 shows some of these methods. 

Lastly, a technique that has been used for many years involves first eutectic or solder attaching high-power devices to small heat spreaders such as molytabs (gold-plated molybdenum tabs that are the same size or slightly larger than the die). Thermally conductive adhesive is then used to attached the die-tab parts to a ceramic or laminate interconnect substrate. 

IPC-SM-785, Guidelines for Accelerated Reliability Testing of Surface Mount Solder Attachments, Nov. 1992. 

IPC 9701, Performance Test Methods and Qualification Requirements for Surface Mount Solder Attachments, IPC, January 2002. www.ipc.org. 

W. Engelmaier, Reliable Surface Mount Solder Attachments Through Design and Quality Manufacturing, International Workshop on SMT Reliability and Manufacturing Issues, 1992... 

M. Tammenmaa, Reliability Analysis of Some Ceramic Lead-Free Solder Attachments, Proceedings of SMTA Pan Pacific Microelectronics Symposium, Kauai, Hawaii, January 25-27, 2005, pp. 161-169... 

There has been a significant worldwide effort to identify suitable lead-free solder candidates to replace eutectic Sn Pb utilized for both the reflow and wave solder attachment of components to PWBs utilized in microelectronic assemblies. Because this effort has consumed much of the initial focus in the lead-free movement within the electronics industry, it is not surprising that the introduction of lead-free solders will represent the initial implementation step. It must be recognized, however, that electronic assemblies wiU, for the most part, be hybrids (i.e., while the solder is utilized for assembly, both reflow and wave solder operations will be lead-free). It is possible in some assemblies that nothing else will be lead-free, including the components and board finishes, as illustrated in Fig. 6. 

Alternatively, a low-melting-temperature solder (e.g., the eutectic Pb-Sn alloy) may be utilized to attach a silicon chip (having high-Pb, Pb-Sn solder bumps) to organic printed circuit boards. The circuit boards are not damaged by the low-temperature solder attachment process. This version of flip chip assembly is referred to as direct chip attach (DCA) or flip chip on board (FCOB) technology. 

Determining the bulk properties of various alloys is a starting point, enabling comparison among Pb-free alloys and baseline Sn Pb solders. In applications, the solder attachment process combines the alloy systems with minor elements from the component termination and from the PWB surface finish to form complex systems. The following sections describe the application of several key alloys and the reliability of the resulting complex systems they form. 

Solder ball solder Attachment solder Activation energy (kJ/mol)... 

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