Bibliographic record
Abstract
This paper reviews the development of chip rework processes at IBM, from leaded bumps on ceramics to lead-free on organic carriers, with emphasis on the latter. Traditionally, when fabricating high performance multichip ceramic modules, the ability to remove one or several chips after testing the fully populated module becomes important in ensuring that it has a full complement of functioning chips. Such a rework procedure has been developed and practiced for years on dies with leaded C4s (Controlled Collapse Chip Connection). It involves removing a die by reflow, before underfilling, and dressing the site using a porous copper block, first soldered and then sheared at room temperature. Later, in an effort to qualify the transition to lead-free solder bumps on ceramic carriers, it became clear that the rework process needed an important modification of the dressing step. Because of the higher stiffness of the Pb-free solder, the usual room temperature shearing of the copper block induced damage to the bonding pads and vias. This led to the development of a hot copper block process that solved this problem, although lead-free did not get qualified on ceramics for other reasons. This improved process was later investigated for reworking bad dies on organic carriers. However, the good performance of the dressing process at removing residual solder was such that on many pads, the solder surface ended below the level of the solder mask thus giving rise to many open connections when joining a new device. This motivated the search for a process that would leave solder residues, after the bad die removal, that would not only be above the solder mask, but also sufficiently uniform to join a new die successfully. Such a modified bare die removal process was developed, without any site dressing being required. Dies 8.5 X 8.5 mm were successfully replaced on a 4-up 55 mm TV carrier, one or two at a time, with passenger dies being underfilled or not before rework. Reliability stressing, DTC 1000 cycles and HTS 1000 h, completed without degradation. Reworking larger dies (17.7 X 17.7 mm) was also demonstrated, with the process being extended to even larger form factor above 20 mm.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.006 | 0.002 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".