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Trace Cracking Problem

Trace Cracking Problem. Pitch Adapter (PA). 2-mil Kapton. ½ oz copper. Nominal 150 m -inch nickel, 10 m -inch gold. Printed Wiring Board (PWB). Nominal 1-mm radius. Cracked traces on PA after bonding. . History. Before fall 2004. ~25% rejection after bonding to PWB.

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Trace Cracking Problem

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  1. Trace Cracking Problem • Pitch Adapter (PA). • 2-mil Kapton. • ½ oz copper. • Nominal 150 m-inch nickel, 10 m-inch gold. • Printed Wiring Board (PWB). • Nominal 1-mm radius. • Cracked traces on PA after bonding. Pitch Adapter Review 1/20/05

  2. History • Before fall 2004. • ~25% rejection after bonding to PWB. • Criterion: < 8 broken traces. • MCM production stopped for unrelated reasons. • Restart in 12/04. • 100% rejection after bonding. • (Almost) every trace is cracked, typically multiple cracks per trace. Pitch Adapter Review 1/20/05

  3. Two Groups of PWB • Nominal 1-mm radius. • “Un-deburred” PWB. • Measurement of profile. • Noticed some surface irregularity. • Gently abrade by hand. • “Deburred” PWB. Pitch Adapter Review 1/20/05

  4. Four Groups of Pitch Adapters Pitch Adapter Review 1/20/05

  5. Minimum Bend Radius Guideline • IPC-2223 guidelines. • 2-mil Kapton and ½ oz copper. • No nickel or gold! • “Flex to install” applicable here. • Also note ultimate elongation at break of 16%. Pitch Adapter Review 1/20/05

  6. Other Bend Radius Guidelines • Radius at least 10x thickness. • PA thickness = 68 mm. • Nominal radius = 1 mm, i.e. ~15x. • Rolled annealed copper grain parallel to direction of bend. • Perpendicular in case of Parlex PA. • Dyconex is electro deposited instead of RA. • Copper layer on neutral bend axis. • Not done here. • Is it possible? Pitch Adapter Review 1/20/05

  7. Intrinsic Bend Capability • Wrap PA around 1-mm aluminum form. • So far only PA Group C. • Add weight until problems show up. • Hairline cracks appeared at 5.5 lbs. • Visible cracks (conductive) appeared at 6.2 lbs. • Cracks became non-conductive at 9.0 lbs. • Conclude no intrinsic problems at 1-mm radius, but … More on this later Pitch Adapter Review 1/20/05

  8. 1-mm Radius Test Jig Pitch Adapter Review 1/20/05

  9. Bend Radius Observation at Teledyne • Use PWB in gluing fixture but no epoxy. • Clamp one side of PA (Group C). • Sweep PA over radius with “wiper blade”. • No additional tension. • Massive trace cracking. • Inconsistent with test jig results. • Trying to understand differences. Pitch Adapter Review 1/20/05

  10. Two Sets of Gluing Fixtures • Teledyne design. • Used in all production so far. • Four almost identical fixtures. • PA stretched during operation. • G&A design. • Used in a few tests. • One fixture. • PA sits in concave mold. • No pulling, hence no stretching. Pitch Adapter Review 1/20/05

  11. Teledyne Fixture Pitch Adapter Review 1/20/05

  12. Teledyne Fixture Design Flaw • Stretch PA ~1.5 mm. • Clear from design drawings. • Confirmed in test. • 1.5 mm / 16% = 1 cm. • PA full width ~6 cm. • Unrestrained part ~1 cm. • Certainly contributor to low yield. Pitch Adapter Review 1/20/05

  13. Recent Test Results Pitch Adapter Review 1/20/05

  14. Conclusion on PWB • Deburring or not is not the fundamental problem. • Similar problems using Group B PA. • Poor radius may be contributing factor. Pitch Adapter Review 1/20/05

  15. Conclusion on PA • Parlex Sep 04 and Nov 04 – no good. • Parlex Apr 04 – better. • Looking into what has changed. • Dyconex much better than bad Parlex PA. Pitch Adapter Review 1/20/05

  16. Conclusion on Fixture • Stretching is very bad. • 1.5 mm is near ultimate elongation. • Teledyne fixture only a contributing factor. • Earlier production yield ~75%. • Recent test with Apr 04 PA OK. • Problem common to all 4 fixtures. • G&A fixture OK with earlier PA, but similar problems with Nov 04 PA. Pitch Adapter Review 1/20/05

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