Die Attach Methods

Die Attach Methods for Chip-on-Board Assembly (COB)

(1) THERMOSET ADHESIVE

PROS: low cure temperature, low modulus of elasticity, high strength, relatively inexpensive, wide process window (bondline, curetime)

CONS: resin bleed, level of thermal/electrical conductivity, limited reworkability, limited internal water vapor (RGA) performance

ISSUES: cure profile, bleedout evaluation, material compatibility, design rules, pot life and storage, dispensing considerations/patterns/voiding, bondline control, placement accuracy/planarity

(2) THERMOPLASTIC ADHESIVE

PROS: low cure temperature, low modulus of elasticity, relatively inexpensive, reworkable

CONS: limited strength, electrical/thermal conductivity, limited internal water vapor (RGA) performance, manufacturing logistics in handling

ISSUES: force, time, pressure, placement accuracy/planarity/bondline, thermal hierarchy

(3) METAL-FILLED GLASS

PROS: high thermal/electrical conductivity, high temperature tolerance, excellent internal water vapor performance (RGA), strength, mid-range modulus of elasticity

CONS: bond line control, cost, non-reworkable, fillet control, die size limitations, high temperature organic burn-out

ISSUES: bond line control, OBO profile, dispense control/voiding, placement accuracy, die size, metallurgy of die backside

(4) GOLD-SILICON EUTECTIC

PROS: high thermal/electrical performance, strength, RGA, temperature tolerance, reworkable

CONS: cost, high modulus of elasticity, limited die size, potential for chip damage, high process temperature, narrow process window

ISSUES: process profile, environment (N2, forming gas), die size, metallurgy (type & oxidation), voiding, collet size/design

(5) SOFT SOLDER

PROS: good thermal/electrical performance, reworkable, good matching for dissimilar CTE's

CONS: special backside metallization required, typically need forming gas and nitrogen atmosphere, die placement issues

ISSUES: level of dioxide in atmosphere, oxidation on surfaces, solder splash during placement, voiding


		Interconnect Methods