Inspecting Si dies on blue tape: the five hardest problems and the results we delivered
No die removal, no flipping: dark cracks, gold bumps, discoloration and broken frames inspected directly on blue tape. Four years and ten sample rounds, from 150 mil down to 5 mil.
Right after dicing, while dies are still on the blue tape, is both the best and the hardest moment for visual inspection. Best, because nothing has to be picked or flipped, so no new damage is introduced. Hardest, because the tape deforms, traps bubbles, and the dies are small and densely packed: any optical disturbance is easily mistaken for a defect.
Over the past four years Shin Shou has run ten rounds of sample validation with a die manufacturer across two product lines. Here are the five key problems we faced and the results we delivered.
Problem 1: bubbles under the tape look exactly like defects
Bubbles between tape and die are unavoidable. In the image their grey levels are very close to real defects such as clamp marks and back-side chipping, so the usual answer is to loosen thresholds — and miss defects. Shin Shou attacked both imaging conditions and judgement logic, so real defects are clearly separated from bubbles.
Problem 2: micro-cracks are thin and shallow
Micro-cracks are among the most critical and least visible die defects. Our in-house imaging method brings out fine cracks that were previously almost invisible.
Problem 3: gold bumps, scratches and brush marks look alike
In ordinary images, gold bumps, deep scratches and surface brush marks are almost indistinguishable. Using our own judgement method, we were able to detect gold bumps on their own in the test samples, sharply reducing brush marks being rejected as defects.
Problem 4: discoloured active areas and broken frame lines
Colour anomalies in the light-receiving area are hard to judge even by eye, and broken frame lines are only a few pixels wide. Both were detected reliably in the samples.
Problem 5: locating 5 mil dies
The smaller the die and the tighter the pitch, the easier alignment fails. We compared imaging at different resolutions and developed inspection software with user-defined layers and two-stage alignment, so even irregular regions are located precisely.
What we delivered
- Dies inspected on blue tape, front and back, without removal or flipping
- Detection of micro-cracks, holes, gold bumps, discoloration, broken frames and more, without rejecting probe marks as defects
- Resolution of 1.25–2.5 μm per pixel, depending on configuration (see note below)
- Dies from 6 mil to 150 mil, with 5 mil alignment and inspection validated
- Manual, semi-automatic and automatic region definition, so changeovers need no reprogramming
These results are built into Shin Shou's Silicon Chip Visual Inspection System. If your dies are hard to see on blue tape, send us samples for a free imaging test.
Note: 1.25–2.5 μm here refers to resolution — the size covered by a single pixel. Judging a defect reliably takes at least 2–3 pixels, so the Silicon Chip Visual Inspection System, at 1.5 μm/pixel, is specified with a minimum detectable defect of >3 μm. Later machines have been optimised to 1.25 μm/pixel, the finest resolution reached in our tests.
