PACKAGING FOR LEAD FREE ASSEMBLY

Introduction: Because of the recent implementation of environmental standards, such as RoHS, WEEE, and others in 2006, the use of a lead-free assembly compatible laminate material is now required. The laminate material must withstand the increased temperatures of lead-free assembly without evidence of delamination of the base material. 

The temperatures for a typical tin-lead assembly process compared to a lead-free assembly have increased 20ºC to 50ºC and thus present unique challenges that require special attention by users during PCB processing, packaging, storage, and lead-free assembly processing. Control of moisture/volatiles in the base material is one of the most critical aspects of manufacturing a lead-free PCB assembly.

The vapor pressure of water increases dramatically from approximately 300 PSI to over 600 PSI resulting in stresses that can easily overcome the bonds at critical laminate interfaces when the Maximum Moisture Content (MMC) is exceeded.  Recent studies by Isola have demonstrated that there is a functional limit to the amount of moisture/volatile that can be allowed in the substrate before the onset of delamination will occur during lead-free assembly.     There is no easy solution for solving moisture/volatile issue. Since laminate materials will absorb moisture/volatile, Isola strongly recommends implementing best practices for PCB packaging, storage, handling, assembly, and rework address this problem.  The objective of this technical bulletin is to offer best practice recommendations to our valued customers. PCB Fabrication and Assembly.

PCB Dry Packaging: Proper packaging of the lead-free compatible PCB is critical. The packaging system must be carefully developed by the PCB fabricator to protect the PCB from atmospheric moisture that may enter the packaging materials by diffusion.  The packaging system should be developed to offer a shelf life of 12 months at ≤40ºC and 90% RH.

Selection of Packaging Materials Selection of the proper packaging material is critical. The packaging engineer must balance many factors including cost and protection in making the proper selection of materials.  The engineer should develop a full understanding of the entire process and packaging system in order to ensure the product is protected properly during shipment and storage. The information contained within this bulletin are a guideline and should not be used to replace a complete understanding of the packaging systems available in the market place.