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Design007-Nov2022

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60 DESIGN007 MAGAZINE I NOVEMBER 2022 I-CONNECT007 Gerry Partida, vice president of technol- ogy at Summit Interconnect, authored a tech- nical paper, "Next Progression in Microvia Reliability Validation—Reflow Simulation of a PCB Design Attributes and Material Struc- tural Properties During the PCB Design Pro- cess," at IPC APEX EXPO 2022, and it's worth revisiting. is significant paper on microvia reliability validation provides a summary of what's been happening in the microvia fabri- cation arena, especially regarding the issue of latent defects in stacked microvias. is paper is available for download here. Partida offers a thorough look at the contro- versy initiated in 1996 when latent electrical defects began showing up in field-deployed boards using microvias. My familiarity with this topic dates to 2000, when IPC organized round robin testing of microvia technologies. All looked good, and HDI technology took off. As evolution would have it, the technol- ogy grew and diversified. But all the new vari- ants were not necessarily tested like the initial round in 2000. As Gerry summarizes, "Today, the industry is facing a similar challenge with microvia reli- ability, especially aer reflowing of the PCB at assembly, during rework, or operating in the field. As with the shortcomings of electrical testing in the past, the industry designed PCBs with microvias without evaluating the thermal properties of the material or the geometries in the design. Fabricators produced the fin- ished goods and evaluated the finished PCB to established performance standards such as IPC-6012. When difficult-to-detect failures occurred post assembly, a test method IPC- TM-650 2.6.27 was established and a caution was added to the IPC- 6012 Rev E in Section 3.6, Structural Integrity. e testing of a D cou- pon via IPC-TM-650 2.6.27 did validate that the finished PCBs were safe for assembly, but it did not stop a fabricator from building a bad design." Analyzing Gerry Partida's 'Significant' Microvia Reliabilty Paper Article by Happy Holden

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