Surface Mount International Conference Proceedings


Author: Shelgon Yee
Company: Solectron Corporation
Date Published: 9/10/1996   Conference: Surface Mount International

Abstract: Tin/Lead surface finish is the most common finish for PCB today and has existed since the beginning of electronic assembly. Hot Air Solder Leveling (HASL) is the most popular process for such surface finish . There is a variety of different processes called Solid Solder Deposit (SSD) for thicker tin/lead coating on PCB pads (several roils thick), such as Optipad, Precision Pad, Sipad etc. Although HASL surface has coplanarity problem (especially for large I/O fine pitch components) , this surface finish is still the most widely used one in SMT assembly. Surface finishes using SSD technology are mainly emphasis on fine and ultra-fine pitch component assembly. The goal is to reduce the overall assembly cost by eliminating the screen printing process. Topics to be covered in the paper include process descriptions, physical characteristics of the finishes, costs and their applications include reflow, flux application, environmental converns, application examples, critical assembly process variables, general SMT assembly concerns and other issues related to the assembly processes. Key Words Tin/Lead Coatings, Metallic Surface Finishes, Hot Air Levelling (HASL), Solid Solder Deposition (SSD)

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