Coated Silver Wire Bond: Reliability of Epoxy Molded Device

Abstract

Free air ball processed using coated silver (Ag) wire is soft similar to gold (Au) wire and enables bonding of stacked devices with over-hangs. The bonded ball shear/pull, dimensions and stitch pull satisfied internal specifications and customer requirements including folded loop. Moreover, reliability of coated-Ag wire bonds when molded using green epoxy mold compound (EMC), containing chlorine (Cl) $\lt15$ppm, sulfur (S) $\lt10$ppm, formulated with ion-catcher and pH between 5 and 7, free of bromine and antimony, revealed reliable bonds. Two of the case studies of coated-Ag ball bonds exhibit:•No failure until 3000h on high temperature storage (HTS) test at $175^{\circ}\mathrm{C}$ and $150^{\circ}\mathrm{C}$•No failure until 1000h on unbiased highly accelerated stress test (uHAST) at $110^{\circ}\mathrm{C}$, 85%RH•No failure until 504h on biased HAST at $130^{\circ}\mathrm{C}$, 85%RH, +20V•No failure until 384h on uHAST, 2000h on HTS at $150^{\circ}\mathrm{C}$, and 2000cycles on thermal cycling at $-55^{\circ}\mathrm{C}$ to $+ 125^{\circ}\mathrm{C}$•Examining EMC formulated with pH 3 to 6 passed 2000h on HTS testing at $175^{\circ}\mathrm{C}$ thereafter bond failed and showed high electrical resistanceThe reported results are based on electrical contact resistance measurement for the condition not to reduce below 10% of time zero bond resistance. The slower failure rate of Ag ball bonds showed EMC formulated with 5 to 7 pH is compatible than formulated with 3 to 5 pH.