Microprobing

Microprobing (Page 2 of 2)

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The glassivation on top of the die surface to be probed is often removed by reactive ion etching prior to probing. Probing a die surface with an intact glassivation is difficult because the glass layer is hard to penetrate with a probe needle. Furthermore, broken glass tends to make the probing area messy, and may even make the electrical contact intermittent, especially when small or narrow metal lines are involved. As an alternative, glass openings may be made on prospective probing points by blasting the glass accurately with a laser cutter.

Fig. 3. Photo of a stand-alone laser cutter

Note: a laser cutter is more often installed atop the microscope of the probing

station since laser cutting is almost indispensable to microprobing

Microprobing almost always requires a schematic diagram and a die lay-out of the device to be effective and efficient. The analyst needs these diagrams to immediately pinpoint critical nodes for probing to isolate the failure site.

During failure isolation, the goal of the analyst is to 'zero in' on the bad component(s). This is difficult, if not impossible, to do without the ability to isolate circuits from each other. The laser cutter is an indispensable tool for this purpose, allowing metal lines to be burned open for convenient isolation of nodes from one another.

If the analyst is not so familiar with the circuit and how it works, microprobing can still be performed as long as a correlation or known good unit is available. Probing in this case proceeds by comparing the voltages or signals at critical nodes of the sample with those of the good unit.

A novice failure analyst must never make his first microprobing attempt on a real sample, since microprobing requires a high degree of skill. Eye and hand coordination, as well as experience, is needed to locate the area of interest, choose an appropriate probing spot, land the needles (see Fig. 4), and exert the correct pressure for good electrical contact. Die scratches and even chip-outs result if probing is not done correctly.

Fig. 4. Photo of a microprobe needle on the die surface

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Decapsulation; Microthermography; LEM; Die Deprocessing; SEM/TEM

FA Lab Equipment; Basic FA Flows; Package Failures; Die Failures

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