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As semiconductor fabrication advances rapidly, conventional probe cards are hitting their test limits. To meet high-density test requirements, MEMS-based wafer-level probe solutions have emerged and are becoming mainstream in high-end semiconductor test. In particular, as 300mm-wafer MEMS probe cards for NAND flash inspection see adoption, FormFactor reports a 37% global market share in this segment, followed by Japanese vendor Apollowave.
Probe cards are widely used to test ICs for smartphones from all major brands, consumer electronics, cloud computing hardware, and automotive chips. Today's products demand thin, light, compact designs, with ICs shrinking in size, growing in functionality, and adding more pins. Given the high unit cost of advanced packaging, testing the die before packaging to identify and mark defective units on the wafer—then discarding those marked units before the back-end packaging process—eliminates unnecessary packaging cost.
The probe cards most widely used in wafer test today are cantilever andvertical probe cards. Cantilever probe cards are especially common, chiefly because individual probes can be replaced for high-current testing. Vertical probe cards, by contrast, deliver higher capability and performance, and the probe material determines their high-frequency probing capability in high-temperature testing.
A probe card is a test interface used mainly for bare-die testing: it connects the tester to the chip and transmits signals to test chip parameters. Users work hard to improve yield and test time and reduce overall test cost—for example, by effectively controlling the frequency of on-line probe cleaning on the tester and various parameters to extend probe card life. But according to Yan Limin, as long as the production line keeps running, demand for the probe card as a consumable will not fluctuate much.
The probes on the card contact the chip's pads or bumps directly, bringing out the chip signals; combined with peripheral test instruments and software control, this enables automated measurement. Probe cards are used before the IC is packaged, performing functional tests on bare die with probes to screen out defective units before the packaging process. Probe cards are therefore one of the key processes with a major impact on manufacturing cost in IC production.
To address incomplete ground-signal capture caused by the small number of probe-to-chip contact points, the design of low-loss surface acoustic wave (SAW) filters emulates solder-joint lead routing: it captures the chip's electrical signals and tests in the frequency domain, meeting the inspection requirements of wafer-level packaging (WLP), chip-scale packaging (CSP), and other packaging processes.
