Scope of this guide
Management version: this defect as cost and risk — the metrics, audit points and claim defence.
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 |
Cost, metrics and defence
| Cost line | Driver | Metric | Lever |
|---|---|---|---|
| Scrap at bake test | Foundry porosity | First-article bake rejection | Supplier quality agreement |
| Rework | Blister escape to customer | PPM by customer | Ship gate on bake audit |
| Chemicals | Over-etch compensation | Etch weight-loss trend | Time-based, not visual, control |
| Delay | Quarantine loops | Days in quarantine | Supplier density certificates |
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
Who pays for porosity blisters?
The casting, when your bake gate and lot tags are in order. Records move the cost upstream.
What KPI predicts blister claims?
First-article bake rejection rate by foundry lot; rising trend = incoming problem.
Is 100% bake testing worth it?
Start with first-article per lot plus audit; escalate to 100% only while a supplier is failing.