What to check when auditing a heat sink supplier, how to qualify a second source cheaply, and which documents actually predict quality problems.
Heat Sink Supplier Audit and Second Sourcing
Direct answer: A heat sink supplier audit should verify five things: that the factory owns the process it claims, that it has a functioning measurement system, that its anodising is either in-house or at a controlled subcontractor, that it tracks die condition, and that it can show first-article and CMM records for comparable parts. Second sourcing is worth doing for any part above roughly USD 20,000 annual spend, but qualify the second source with a small batch rather than a full transfer.
The five things that actually predict quality
| Check | What good looks like | What a weak supplier shows |
|---|---|---|
| Process ownership | Presses, CNC and anodising either owned or with a named, audited subcontractor | Vague answers about where the anodising happens; no subcontractor list |
| Measurement system | Calibrated CMM, surface plate, roughness tester, with calibration records | Calipers only; no calibration certificate; measurement done by the inspector's judgement |
| Die condition tracking | A log per die: tonnes run, re-polish dates, bearing rework history | No record; die condition discovered only when parts fail |
| First-article records | FAI reports for similar parts, with the fixture and gauge identified | No FAI, or an FAI that only lists nominal dimensions with no method |
| Flatness control | A flatness gauge or CMM routine applied to the contact face with a defined sampling plan | Flatness checked by eye against a straight edge, or not checked at all |
Notice what is not on this list: factory size, number of machines, and certifications on the wall. Those correlate weakly with delivered quality. What correlates strongly is whether the supplier can produce a measurement record and a die log for a part similar to yours.
Questions to ask during the audit
- "Show me the CMM report for the last three lots of a heat sink with a flatness callout." If they cannot produce three, they do not SPC the feature. This single question separates serious heat sink factories from general machine shops.
- "Where is anodising done, and when were you last at that facility?" Anodising is the most common quality escape in aluminium heat sinks: colour mismatch, thickness variation and masking errors. A supplier who subcontracts it without oversight is passing an uncontrolled process to you.
- "How do you track die wear, and what triggers a re-polish?" A die that drifts makes fins thicker, which changes weight and thermal resistance. Without tracking, drift is discovered by the customer.
- "What is your scrap rate on heat sinks with a 0.05 mm flatness callout?" A number below 2% is either excellent or not measured. A number around 4-8% is realistic and honest. Refusing to answer is an answer.
- "Which of your machines would run my part, and what is its current load?" This predicts lead time more accurately than any promise. A part scheduled on a machine at 95% utilisation will be late.
- "Can I see the packing area and the drop-test procedure?" Fin damage happens in packing, not machining. The packing area tells you how much they care.
Remote audit: what works and what does not
Most buyers will not fly to Dongguan for a first order. A remote audit is imperfect but useful if it is structured.
- Ask for a live video walkthrough, not a recorded video. A recorded video is a production. Ask them to walk to a specific machine and show the job currently running.
- Ask for the calibration certificate of a specific instrument, today. Photos with a dated note beside the instrument.
- Send a test part you have measured yourself. Ask them to measure it and return the report. This checks the measurement system, which is the only thing that matters.
- Ask for a small paid trial order before the main order. Fifty pieces shipped and dimensional-report checked will tell you more than three video calls.
When second sourcing is worth the cost
| Annual spend on the part | Second source? | Reasoning |
|---|---|---|
| Under USD 5,000 | Usually not | Qualification cost exceeds the risk |
| USD 5,000-20,000 | Optional | Worth it if the part is on a critical path or the single source is small |
| USD 20,000-100,000 | Yes | A line stoppage costs more than qualification |
| Above USD 100,000 | Yes, and keep it warm | Run 10-20% of volume continuously through the second source so the relationship and tooling stay live |
The common mistake is to qualify a second source and then never order from them. A dormant source is not a source: the tooling sits idle, the operator forgets the part, and when you need them in a crisis they behave like a new supplier.
How to qualify a second source without duplicating tooling cost
- Own the tooling. If you own the die, transferring it is a logistics exercise, not a capital one. This is the strongest reason to pay for tooling separately.
- Transfer the die, not the design. A second source running your die produces the same profile, so the thermal and dimensional risk is confined to machining and finishing.
- Qualify on machining only first. Buy extruded blanks from the first source, machine and finish at the second. This isolates the variable you are testing.
- Run a parallel batch of 5-10% of volume. Compare CMM results and flatness, not just visual appearance.
- Compare the finished part thermally, once. A new machining route can change the contact face finish and therefore the thermal result, even with identical geometry.
Frequently asked questions
Is ISO 9001 enough?
It is a starting filter, not evidence. ISO 9001 certifies that a quality system exists on paper. Ask for CMM records and a die log, which show whether it operates.
Should I audit the anodising subcontractor too?
If the finish is cosmetic or the part is visible, yes. Anodising is where colour and thickness disputes originate, and it is usually a separate facility from the machine shop.
How long does second-source qualification take?
Four to eight weeks for a machined heat sink with an existing die, and eight to twelve weeks if a new die is involved. Add two weeks for a full thermal and reliability validation.
What is the strongest single indicator of a good heat sink supplier?
Whether they push back on your drawing. A supplier who silently accepts a 0.02 mm flatness callout on a 300 mm base with a thin fin has not understood the part. A supplier who asks why you need it, and offers a cheaper alternative that meets the actual interface requirement, is the one to keep.
Ask for the audit pack for any part number: process route, subcontractor list, die log and the last three CMM reports. We will send it before you ask twice.
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- Custom Heat Sink MOQ and Lead Time by Process
- Heat Sink Extrusion Die Cost and Tooling Amortisation
- Heat Sink RFQ: What to Send for an Accurate Quote
- Heat Sink Tolerance and Flatness: What to Specify
- Heat Sink Surface Finish Options and Cost Impact
- Heat Sink RoHS, REACH and UL Compliance Explained
- Heat Sink Volume Pricing: How Breakpoints Really Work
- Heat Sink Prototype and Sample Service: What to Expect
- Heat Sink Packaging, Shipping and DDP Terms
- Heat Sink Thermal Test Report: What the Data Package Contains
