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Knowledge Base/Part Approval Process (PAP): How to Substitute PPAP
Supply Chain Quality6 min read

Part Approval Process (PAP): How to Substitute PPAP

This article highlights a critical challenge faced by a semiconductor manufacturer: a supplier's component Cpk report of 1.08, a quality level fundamentally unacceptable for their industry, creating a significant impasse. It reveals the substantial divergence between the stringent part validation standards of the semiconductor sector and the traditional automotive PPAP, particularly concerning yield requirements.

That Day the CPK Report Came Out, the Room Was Silent for Three Seconds

I remember years ago, when we were introducing a critical resistor for a new model, PAP was routinely conducted before mass production. The PPAP report from the supplier showed a Cpk value of 1.08. In the meeting room, the yield manager was livid, and the entire PM team instantly fell silent. Think about it, what does a Cpk of 1.08 mean? By the most stringent standards, the DPMO was already 6210! We're a semiconductor factory; how could such a level possibly pass? But the supplier confidently asserted that their process was stable and the data was fine. We were really stuck there, not knowing what to do.

What Went Wrong

To be honest, our semiconductor factory's Part Approval Process (PAP) is essentially a variation derived from the automotive industry's PPAP (Production Part Approval Process). However, PPAP's validation standards are often insufficient for an industry like semiconductors, which pursues extreme yield rates. Automotive parts might accept tens of DPM, but for our chip shipments, the goal is a few DPM or even PPB levels. If we merely verbatim requested suppliers to submit a document complying with PPAP specifications, and then approved it upon seeing a Cpk of 1.08, that would be playing with fire. Frankly, PAP shouldn't just be a document review; it should be a "tool" to ensure part quality meets our own stringent standards.

What We Actually Do

So, we later developed our own "alternative PPAP" PAP strategy. It's actually not that complicated; the focus is on "communication" and "data analysis."

  1. Tailored Quality Requirements: Early in the project, we clearly communicate our DPMO targets with the supplier. For example, if your product target is 500 DPMO, then your parts cannot accept a level of 6210 DPMO. We explicitly require suppliers to provide yield data substantiating that our target DPMO is met during PAP submission, rather than just stating compliance with PPAP.
  2. Key Aspects of Data Interpretation: Upon receiving the supplier's PPAP report, in addition to the Cpk value, we delve deeper into X-bar & R charts, Run charts, and even request raw measurement data. For instance, if a supplier presents a Cpk of 1.67 (approximately 0.6 DPMO), which looks excellent, but their X-bar chart shows a drifting trend in the process center point, then this Cpk might only be a short-term performance, carrying long-term risks. In such cases, we would require them to propose an improvement plan or increase the frequency of process monitoring.
  3. On-site Audits and Process Confirmation: Frankly, just reviewing documents isn't enough. We regularly send personnel to the supplier's site for on-site audits, confirming whether their process control, measurement equipment calibration, and even personnel training are truly in place. I recall one instance where we discovered that a certain supplier's inspector, during measurement, had the instrument placed in a position that affected the readings—such details would never be written in a document.

The Most Common Pitfall

The most common pitfall is treating PAP as a "document checklist" process. Many procurement or PMs, to meet project deadlines, reluctantly allow suppliers to submit documents as sufficient. What's the consequence? After mass production, unstable part quality is discovered, leading to frequent failures, affecting the yield of the end product, and even resulting in customer complaints. At that point, the time and money you spend will undoubtedly be several times what you would have spent on PAP. I remember one time, in a rush to launch a new product, we slightly loosened the PAP review for a non-critical part. As a result, after shipment, customer complaints poured in because that part's tolerance was larger than stated in the document, causing gaps during assembly. Upon investigation, we found that the supplier had secretly adjusted parameters in their process, but these were not updated in the documents.

One Thing You Can Do Today

Next time you receive a PAP report, don't just look at the Cpk; be sure to ask the supplier for an X-bar & R chart.

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