Scope of this guide
Senior version: the fix set with parameter windows, boundary cases and the discipline that keeps them fixed.
This series answers a top recurring question from finishing forums with platingclub line practice. Parameters are industry-standard starting ranges — confirm against your supplier TDS.
Triage: symptom → confirm → first move
| Blister pattern | Likely root | Confirm by | First move |
|---|---|---|---|
| After plating bake only | Sub-surface porosity out-gassing | 200 °C re-bake test | Quarantine casting lot |
| Random single blisters | Oil or wax under deposit | Blister cross-section | Pre-clean audit |
| Edges and thin walls | Over-etch or acid dwell | Etch weight loss check | Cut acid time, verify strike |
| On flat faces in rows | Air trapped by rack angle | Position map | Re-rack angle 10–20° |
| Whole lot, every load | Casting gas content | Density / lot tag audit | Push back to foundry |
The fix set
- Fix 1 — bake gate — 100–110 °C × 1–2 h pre-plate bake; 200 °C test bake for release of new lots
- Fix 2 — strike discipline — Copper strike first on zinc; never acid pickle raw zinc diecast
- Fix 3 — etch control — Mild alkaline clean; acid contact seconds only, by weight-loss check
- Fix 4 — transfer wet — Never let parts dry between stages; dry film = blister seed
- Fix 5 — supplier gate — Bake-test first articles of every new casting lot; density audit on suspicion
Case method
A hardware line saw blisters appear only after its own bake step. The 200 °C test bake on first articles of each new casting lot moved rejection upstream: foundries with high gas porosity were rejected before plating, and blister escapes to packing fell to single digits per month. (Method illustration: keep your own bake window data.)
Engineer notes
- One variable per corrective action; verify by the confirm-by column.
- Records beat memory: log every trial on the tank card.
- Escalate when two consecutive actions fail — that is a senior call.
Safety: bake ovens hold hot parts and hydrogen risk from pickled parts is real. Heat gloves, face shield at door, and never load pickled zinc straight into a hot oven.
FAQ
Copper strike parameters on zinc diecast?
Alkaline copper strike, low CD start, full immersion contact; check first-article adhesion by bend test.
How do I set a supplier density gate?
Agree a minimum density per part family with the foundry; verify by weigh-measure on samples per lot.
When is it the bath, not the metal?
When blisters cross casting lots and follow bath events — filter hours, cleaner titration, oil skims.