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Lead Free Qualification

The qualification of a lead-free assembly process is no different from any other kind of process investigation. You must first understand the characteristics of the material sets of choice, followed by investigations on sample / representative hardware. Only then can you validate the assembly process on actual product relative to existing standards of quality and acceptability. To these ends, PAL provides a qualification package in three phases to assist manufacturers in their transition to lead-free assembly.

Phase I: Materials Screen using Ion Chromatography (IC) and Surface Insulation Resistance (SIR)

This first phase is intended as a screening methodology for selecting lead free materials such as solder pastes, fluxes, and cored wire solder products. The testing is performed per J-STD-004, IPC-TM-650 methods 2.3.28 for IC and 2.6.3.3 for SIR. The test vehicle utilized for this phase is the IPC B-24 board. The test matrix includes a sufficient sampling of processed B-24 boards to give statistical strength to the analysis plus 1 or 2 unprocessed boards for baseline purposes. The boards should be manufactured with the client's preferred laminate, solder mask, and metalization.

Phase II: Lead-Free Process Investigation using IC, SIR, and X-sectioning

After the lead free candidate materials have been chosen, it must be determined how the materials will work in a factory setting. A standard test assembly, such as the SMTA Saber board or Umpire board, is processed through the candidate assembly processes. The test vehicles contain a variety of components representative of mainstream hardware, and should be fabricated using the assemblers chosen material sets. The residues existing on the test assemblies are characterized using ion chromatography per IPC-TM-650, method 2.3.28. The standard test vehicles are designed for SIR testing and can be tested per IPC-TM-650, method 2.6.3.3 (static 85/85) or method 2.6.3.1 (cyclical / condensing). In addition to IC and SIR testing, cross sectional analysis is done to study solder joint composition, wetting angles and overall solder joint appearance. The sample sizes are chosen to be consistent with IPC protocols (J-STD-001C, Appendix B).

Phase III: Lead-Free Process Qualification

No matter how well a material works in lab tests, it is important that actual product be built with the new materials and the new manufacturing processes. IC is used to determine the residue level at the time of qualification, which is critical for later possible process optimization work. Cross sections of representative solder joints can be judged relative to the customers defined quality metrics, and per IPC guidelines. The actual "qualification" should be a life test on the product using the customer's established quality metrics. Alternatively, the process can be qualified to J-STD-001, using the test vehicles specified in that document.