PRINTED CIRCUIT BOARD CONSIDERATIONS FOR LEAD FREE ASSEMBLYAuthor: Dale Lee
Company: Plexus Corporation
Date Published: 9/25/2005 Conference: SMTA International
Current tin/lead solders melt at 183oC with a SMT reflow process temperature of the PCB up to 235oC. The SAC alloys have a melting point of around 217oC with a SMT process temperature for the PCB of up to 260oC and potentially up to 270oC for wave solder and rework processes. These elevated temperatures place additional stress on current printed circuit board materials that were developed to support lower tin-lead assembly process temperatures. With repeated exposure to the lead free solder process assembly temperatures, the laminate materials begin to degrade resulting in discoloration and delamination.
In addition to lead, several brominated flame retardants are also identified for elimination in the RoHS legislation. The paper provides clarification on specification for selection and recommendation of requirements for printed circuit boards (PCB).
Key Words: Lead Free Laminate, Finish, Halogen Free, Tg
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