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Die Attach Process Development Using B-stageable Epoxies

Die Attach Process Development Using B-stageable Epoxies. Elgin F Bravo May 11th 2001 Advisors Dr. R. Chung Randall Walberg SJSU NSC. Motivation. Reduce package size

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Die Attach Process Development Using B-stageable Epoxies

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  1. Die Attach Process Development Using B-stageable Epoxies Elgin F Bravo May 11th 2001 Advisors Dr. R. Chung Randall Walberg SJSU NSC

  2. Motivation • Reduce package size • Ability to wirebond close to edge of die • Easy to die attach small dies • Dies smaller than 1mm2 • Reduce cycle time • Increase profits • Innovative • New to industry

  3. Outline • Objectives • Last semester accomplishments • Background on B-Stage epoxies • Literature review • Percent conversion • Infrared Absorption Spectroscopy • Moisture Sensitivity Level • MSL results • Conclusion • Future work

  4. Objectives • Determine process feasibility and ease of manufacturing • Coating of die with b-stage epoxy • Die attach die onto leadframe • Elimination of epoxy bleed • Study moisture and heat sensitivity of B-stageable epoxies when used as die attach materials in leadless leadframe packages.

  5. 1mm 1mm B-Stage epoxy Standard epoxy Last Semester Accomplishments

  6. Background on B-stageable Epoxies • A-stage --> unpolymerized --> 0% conversion • B-stage --> some polymerization --> 28 ~ 45 % conversion • C-stage --> mostly polymerized --> 90% conversion

  7. Literature Review • Percent conversion determines bond reliability • Higher degree of conversion lower bond reliability • Lower degree of conversion higher bond reliability

  8. Determining % Conversion • Differential Scanning Calorimetry (DSC) • dX/dt = K(T) x f(X) • k(T) reaction rate constant • X fractional conversion • t cure time • Infrared Absorption Spectroscopy • Epoxide + Hardener = polymer chain

  9. NaCl disk, 2.5 mm thick Detector Thin layer of epoxy ~ 0.5mm Infrared Absorption Spectroscopy E = h  = c/  = 2.5e-4 to 25e-4 cm

  10. % T R A N S M I T T A N C E Infrared Spectroscopy Functional group

  11. Chemical Reaction in Epoxies O || R1 - C = C - R2 + R3 - C - O - O - H ---> Alkene Peroxyacid O H / \ . . | • R1 - C - C - R2+ H - N - R3---> R1 - C - CH2 - R2 | | H H2N - R3 Epoxide Amine Polymer chain (hardener)

  12. Components in B-stageable Epoxies

  13. CH2 CH CH2 Bond Structure of Epoxide Molecules BisphenolA/ Epichlorohydrin epoxy Cresol novolac epoxy

  14. Infrared Transmittance as function of Curing TimeSumitomo 4291 Epoxide C-C Amine (N-H) Carboxyl (COOH)

  15. Infrared Transmittance as function of Curing Time Epoxide C-C Amine (N-H) Carboxyl (COOH)

  16. Curing time & temperature

  17. Moisture Sensitive Levels • Level 1: 168 hrs 85C / 85% Relative Humidity (Excellent) • Level 2: 168 hrs 85C / 60% Relative Humidity (Good) • Level 2A: 150 hrs 60C / 60% Relative Humidity (Satisfactory) • Parts go through reflow oven reaching a max temperature of 235C • Packages assembled onto PCB are reflowed at ~ 220C

  18. Leads Die Cu substrate Top sonoscan view of a Package

  19. Sonoscan Results MSL 1 Front view Back view

  20. Sonoscan Results MSL 2 Front view Back view

  21. Sonoscan Results MSL 2A Front view Back view

  22. Conclusion • Process was concluded to be feasible • Die coating • Die attach • Elimination of epoxy bleeding • Infrared absorption spectroscopy might not be reliable for this type of study • Both B-stageable epoxies fail all three Moisture Sensitivity Levels

  23. Future Work • Work together with suppliers to improve MSL rating to at least MSL 2 • Thermal modeling • Determine how well epoxy dissipates heat • Electrical testing • Determine electrical conductivity of epoxy

  24. Acknowledgements • Dr. Richard Chung • Randall Walberg • Dr. Roger Terrell • National Semiconductor

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