STEP 5 • WIRE BONDING

Wiring it up

The most common approach is thermocompression ball-wedge bonding, usually with gold wire: a ball is formed at the wire's end on the die's bond pad, then — after a stitching process — the wire is placed on a lead-frame post and cut.

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Heat and pressure alone form a solid metal-to -metal bond — no solder required.

AN ALTERNATIVE

Flip-chip: skip the wires

Flip-chip bonding eliminates leads entirely, connecting the die to its substrate through solder bumps instead.

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It offers better electrical and density performance, costs less, and enables rapid MEMS prototyping — attaching or removing a die is as simple as locally heating the substrate to reflow the solder.

No wires to route means less parasitic capacitance and less crosstalk.

FLIP-CHIP IN ACTION

Flip-chip onto glass

1. Coat Deposit photopolymer on the movable polysilicon MEMS plate

2. Prepare Fabricate a substrate with matching bonding pads

3. Bond Flip-chip bond the MEMS device to the substrate

4. Release Free the movable MEMS plate in an acid bath

The photopolymer protects the moving structure right up until the final release step.

UNIT 31 STUDY COMPLETE

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Ready for the Fab Challenge?

You've covered Wiring & Flip-Chip.