Circuits Assembly - November 2008 - (Page 30)

Cover Story to determine the level and rating, assigned based on Table 3. The requirements for a test report to be considered substantially complete include: • Test conditions. • Test duration. • Test vehicle. • Test results. • Pass/fail indication. There are three categories within a typical test report: 1. The “Mitigation Strategy Review Status” provides the summary of the lead finish analysis and areas of concern. 2. The “Qualification Test Review Status” identifies whether whisker testing was adequate. 3. The “Overall Judgment Status” helps clarify the combined whisker risk for the product. Table 4 (online) shows results of an analysis of an end-product with 1426 line items. It is recommended a component engineering team familiar with the process and industry standards assist in Sn-whisker risk assessment. If component selection with the appropriate lead finish does not adequately reduce whisker risk, the OEM may want to consider conformal coating. Conformal coating an assembly will help mitigate tin whiskers; however, it will not eliminate tin whisker growth. Tin whisker growth may either occur under the conformal coating or may grow through the coating. Tin whiskers that grow through the conformal coat typically do not grow back into the coating. Product Conversion Several basic steps should be considered when converting a product to RoHS compliance. The engineering team should work with the supply chain and manufacturing organization throughout the conversion process: 1. Select a product representative of your other products in Table 3. Requirements for Test Report to be Considered Substantially Complete Acceptable (All Must be Yes) Acceptable surface finish technology If required, acceptable mitigation technology applied Surface finish acceptable for product class JEDEC or iNEMI test / accept criterion used If required, complete test report received Test report and accept data match standard requirements Test report clearly states samples passed test E4 test and accept criterion used. 2d party test accept criterion used that closely matches JEDEC, iNEMI or E4 Substantially completed test report received Test report and accept data substantially matches standard requirements Test report or test data indicates samples passed test Test in process with no failures to date – expected completion date has been given Moderate Concern Strong Concern Unacceptable surface finish technology Unacceptable or no mitigation technology applied Surface finish unacceptable for product class “Home brew” or no test accept criterion cited terms of the supply chain, component/PCB technology, and application. 2. Conduct a supply chain analysis to verify all components are RoHS compliant. This may highlight issues in the supply chain such as: • Vendor readiness. • Unacceptable temperature ratings (260°C is required). • Unexpected presence of cadmium, mercury and hexavalent chromium. • Moisture sensitivity levels (MSL) that drop 1 to 2 levels. • Nonpreferred component surface finishes (tin whisker risk or solderability issues). • EOL/component lifecycle issues. 3. Select a PCB laminate and surface finish. • Laminates: MSL are critical. • Surface finish: OSP, ENIG, ImAg and Pb-free HASL. 4. Collect the following in-process data and compare with the SnPb version of the assembly, if available: • Inspection yields including visual inspection, AOI and AXI. • ICT, flying probe and functional test. • Forced rework of a through-hole component and BGA is recommended to validate the rework process. 5. Engineering should review the product’s original testing documents, and run the compliant product’s tests accordingly. 6. Select from the following tests as appropriate. It is strongly recommended the Pb-free assembly be subjected to the same tests used for the SnPb assembly, which may include additional test(s) to those recommended in Table 5. Results from these tests will help guide the OEM to do further studies, submit to the FDA or redesign the product accordingly. In the conversion process, the first step is to scrub the BoM and identify compliant components. Some key data to capture: • OEM part number. • Description. • Manufacturer. • RoHS-compliant part number. • Date code, if used to identify compliance. • Some vendors did not change their part numbers, but identify compliance by date codes greater than their compliance date. • Supplier compliance data sheet/material content. • Homogeneous level, if available. • Y/N at a minimum. Table 5. Test Recommendations Test Criteria Assessed Solder joint strength BGA joint strength PCB and joint integrity Solder joint metallurgy / intermetallic compound (IMC) Ionic levels/overall cleanliness Long-term reliability Solder joint integrity Product-specific application Pull tests of representative SMT components Shear tests of BGAs Cross-sections of SMT and PTH Components SEM or EDS Ion chromatography SIR testing of SMT, PTH, and touchup chemistry (SIR cards) Thermal cycling per IPC-9701 Mechanical shock, vibration, HALT No test report received Test report and accept data do not match standard requirements Test report ambiguous if samples passed test, or samples did not pass test Test not started or no intention of performing test Test has been completed 30 Circuits Assembly NOVEMBER 2008 circuitsassembly.com http://www.circuitsassembly.com

Table of Contents Feed for the Digital Edition of Circuits Assembly - November 2008

Circuits Assembly - November 2008 Contents Caveat Lector Industry News Market Watch Talking Heads Focus on Business On the Forefront Screen Printing Better Manufacturing RoHS Conversion for Medical Devices Supporting Full-Service Customer Requirements at the Regional EMS Level Speed Thrills Tech Tips Wave Soldering Process Doctor Pb-Free Lessons Learned The Defects Database Getting Lean Materials World Product Spotlight Ad Index Assembly Insider Technical Abstracts

Circuits Assembly - November 2008

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.