Tom
10-29-2002, 07:35 AM
IPC Advanced Study Guide Page Reference: Page 24, Section 1.3
When selecting an alternative solder finish, the designer must consider the handling and storage requirements of each finish. Organic protective coatings have reduced shelf life, require special handling, but offer extremely flat surfaces and good solderability when fresh. Gold plated boards are much more robust in storage life and less handling critical, but are far more expensive based on gold’s market value. The gold may also have issues with solder joint integrity as the lands get smaller. Solder with excess gold in the joint causes solder embrittlement which affects long term reliability.
With the advent of increasing use of lead-free solder or no-clean solder fluxes, the issue of leaving flux residue on the board and processing assemblies at higher process temperatures (to reflow the non-lead solders) become key decision factors. This factors impacts not only the surface finishes, but also the laminate itself. A great deal of research is still in progress to look for lead-free solders that process at a lower temperature to improve the reliability of the components and the attachment process, so that the products are not subjected to these extreme temperatures during the assembly operation.
See the chart below to evaluate the various properties of alternative surface finishes.
When selecting an alternative solder finish, the designer must consider the handling and storage requirements of each finish. Organic protective coatings have reduced shelf life, require special handling, but offer extremely flat surfaces and good solderability when fresh. Gold plated boards are much more robust in storage life and less handling critical, but are far more expensive based on gold’s market value. The gold may also have issues with solder joint integrity as the lands get smaller. Solder with excess gold in the joint causes solder embrittlement which affects long term reliability.
With the advent of increasing use of lead-free solder or no-clean solder fluxes, the issue of leaving flux residue on the board and processing assemblies at higher process temperatures (to reflow the non-lead solders) become key decision factors. This factors impacts not only the surface finishes, but also the laminate itself. A great deal of research is still in progress to look for lead-free solders that process at a lower temperature to improve the reliability of the components and the attachment process, so that the products are not subjected to these extreme temperatures during the assembly operation.
See the chart below to evaluate the various properties of alternative surface finishes.