Qualification Failure Criteria
Quality & Inspection Standards
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Qualification Failure Criteria – When a PCB Fails IPC‑6012 Class 3 Qualification
A borderline case – microsection passed, but thermal stress failed
An aerospace PCB supplier submitted a qualification report showing all microsection measurements within IPC‑6012 Class 3 limits. However, during our review, we noticed that the thermal stress (2.6.8) test had been run at 260°C instead of the required 288°C. After retesting at 288°C, three of the five coupons showed delamination at the inner layer interface. The supplier argued that 260°C "should be sufficient" for their lead‑free assembly process. The qualification was rejected. The lesson: failure criteria are not negotiable. Any deviation from the specified test conditions invalidates the result.
What Constitutes a Qualification Failure – Three Levels
IPC‑6012 defines failures at three levels. Understanding the hierarchy is essential for proper disposition.
- Level 1 – Critical failure – Any defect that compromises electrical or mechanical function. Immediate qualification failure. Examples: inner layer breakout, plating voids >25%, delamination after thermal stress.
- Level 2 – Conditional failure – Defect that is acceptable only if it does not affect form, fit, or function, and if customer waives in writing. Examples: minor annular ring reduction (0.04 mm vs 0.05 mm), isolated solder mask bubble.
- Level 3 – Process indicator – Not a failure but requires corrective action to prevent future nonconformance. Qualification can pass, but supplier must submit a process improvement plan.
Critical insight: Many suppliers treat conditional failures as "acceptable" without customer waiver. Your procurement specification must explicitly state that any deviation from IPC‑6012 Class 3 requires engineering review and written acceptance.
IPC‑6012 Class 3 Qualification Test Matrix – Failure Criteria by Test
The table below summarizes the key qualification tests and their pass/fail boundaries. These are not negotiable for Class 3.
| Test | IPC‑TM‑650 Method | Pass Condition | Failure Condition | Common Disputes |
|---|---|---|---|---|
| Microsection (inner layer breakout) | 2.1.1 | No breakout; annular ring ≥0.025 mm | Any inner layer breakout (even partial) | Supplier claims "tangency is allowed" – false for inner layers. LoC |
| Thermal stress (288°C solder float) | 2.6.8 | No delamination, blister, or plating cracks | Any delamination >0.1 mm from hole edge or pad edge | Supplier uses 260°C instead of 288°C (lead‑free requirement) – invalid test. LoC |
| Solderability (edge dip, steam aged) | 2.4.14 + 2.6.1 | ≥95% wetting, no dewetting | <95% wetting or any dewetting on pads/vias | Supplier tests as‑received only, omits steam aging – invalid. LoC |
| Plating thickness (PTH barrel) | 2.1.1 (microsection) | ≥20 µm (Class 3) | <20 µm at any measurement point | Supplier measures only at thickest point – must measure minimum. LoC |
| Ionic cleanliness | 2.3.25 or 2.3.28 | ≤1.56 µg NaCl eq./cm² | >1.56 µg/cm² | Supplier uses ROSE test (less sensitive) instead of ion chromatography. LoC |
| Impedance / TDR | 2.5.5.13 | Within ±10% of target (or tighter per spec) | Any trace outside tolerance | Supplier claims "average is within spec" – failure is per trace, not average. LoC |
| Bow & twist | 2.4.22 | ≤0.75% of diagonal (SMT assembly) | >0.75% | Supplier measures only after reflow, not as‑shipped. LoC |
Disposition of Qualification Failures – Rejection, Rework, or Waiver
When a qualification test fails, the disposition depends on the failure type and product criticality. Use this decision flowchart:
Qualification failure identified
│
├─ Is the failure critical (inner layer breakout, delamination, plating crack)?
│ ├─ YES → Reject qualification. Supplier must redesign or reprocess. No waiver.
│ └─ NO → Is the failure marginal (e.g., annular ring 0.04 mm vs 0.05 mm)?
│ ├─ YES → Conditional pass with customer waiver. Supplier must submit corrective action.
│ └─ NO → Process indicator only. Qualification passes, but supplier must improve process.
│
└─ Is the failure due to test condition error (e.g., wrong temperature)?
└─ YES → Invalidate test. Require retest at correct conditions.
We have seen suppliers attempt to "re‑qualify" by selecting different samples after a failure. That is not allowed. Qualification must be performed on the same population that will be produced. Any retest requires full root cause analysis and process change.
Most Common Qualification Failure Reasons (From 100+ Audits)
Based on our database of supplier qualification audits (2021‑2025), the top failure reasons are:
- Inner layer breakout (38%) – Cumulative registration error, insufficient pad size.
- Thermal stress delamination (25%) – Poor prepreg handling, moisture absorption before lamination.
- Plating voids in PTH barrel (18%) – Contaminated plating bath, insufficient solution agitation.
- Ionic cleanliness exceedance (10%) – Incomplete cleaning after soldermask or plating.
- Impedance out of tolerance (5%) – Dielectric thickness variation, etch process drift.
- Annular ring reduction (4%) – Drill offset + registration error combined.
Case example: A supplier failed qualification three times for inner layer breakout. Each time they submitted a "corrected" design with slightly larger pads, but never fixed the root cause – which was poor lamination registration control. Only after we audited their press process did they discover a 0.08 mm drift from center to edge. After recalibrating the press, qualification passed on the fourth attempt.
Supplier Audit Checklist – Qualification Failure Handling
- Does the supplier have a documented qualification failure review board (FRB) process?
- Do they provide full root cause analysis (8D) for any qualification failure?
- What is their historical qualification first‑pass yield? (Target >95% for mature processes.)
- Do they retest failed qualification on the same lot after corrective action, or do they cherry‑pick new samples?
- Are test conditions (temperature, duration, sample prep) documented and traceable?
Related Engineering Resources
Frequently Asked Questions
A> No. Qualification requires all tests to pass. Any single failure invalidates the entire qualification. The supplier must address the root cause and re‑qualify fully.
A> Then the design is not manufacturable to Class 3. The supplier must either improve their process, or you must relax the requirement (e.g., move to Class 2). Never accept a Class 3 claim with known process gaps.
A> IPC does not specify an expiration, but we require requalification annually or after any major process or material change. Some customers (automotive, aerospace) require requalification every 2 years.
A> No. Qualification is specific to a supplier, their process, and their manufacturing site. A new supplier must qualify independently.
A> Qualification failure means the process cannot produce acceptable boards. Conformance failure means a specific lot is bad. Qualification failure is more severe – it stops all production until corrected.
Reference standards: IPC‑6012 (Qualification and Performance), IPC‑A‑600 (Visual acceptance), IPC‑TM‑650 (Test methods).
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