CpK on a manufactured assembly?

FloridaST

Starting to get Involved
#1
Greetings, I'm new to the QA world and a customer is requesting a CpK on a manufactured box build assembly as part of their PPAP. Now I'm familiar with doing a CpK on items with actual measurable upper and lower limits but I'm a bit unsure as to where to start with this request. Essentially we're placing a circuit board into an enclosure and then potting it. Any advice would be appreciated. Thanks!
 
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FloridaST

Starting to get Involved
#3
Can you provide more details. What measurable output or characteristic is the customer asking you to calculate Cpk for?
The customer clarified and realized they asked for a CpK on the wrong thing.

Let me ask you this, who determines the measured characteristic when a CpK is requested? These aren't our products or designs, we simply build to specification. I'm not strong in this area so I really couldn't give much help to the customer.
 

Golfman25

Trusted Information Resource
#4
The customer clarified and realized they asked for a CpK on the wrong thing.

Let me ask you this, who determines the measured characteristic when a CpK is requested? These aren't our products or designs, we simply build to specification. I'm not strong in this area so I really couldn't give much help to the customer.
It should be based on your customer's needs.

If you get to pick, then pick the easy one. :)
 

ScottK

Not out of the crisis
Staff member
Super Moderator
#5
Echoing Golfman… it's based on the customer needs - if you are building to their specification then they should specify which characteristics are critical to quality (CTQ) and require some sort of capability analysis.
 

ncwalker

Trusted Information Resource
#6
Customer needs is ONE aspect of it.

The purist answer is - you should do it on every measurable process you have. Who WOULDN'T want to know how capable they were on everything? More data means better data driven decisions, right?

Unfortunately, they cost to perform. AND some of your tolerances are really easy to hit. So you really want a strategy - let's do them on the things that count.

One of these is what your customer identifies as critical, as everyone has said. But there's a few more sources:

1) YOU may know some items are also critical. Your customer may not be the expert on your product.

2) There may be some features that are very difficult for whatever reason. They may not be critical, but they are still toleranced and just very tricky to make.

3) There may be some features that have little meaning to the part. They may not even be dimensioned or specified. But ... they may give you easy to measure metrics that the process is behaving.

So when you are deciding what to do a capability study, these are good things to think about. By no means do you have to do all of them, there should be some logic surrounding what you pick.
 
#7
You may start to do Cpk study of solder paste volume such as the thickness characteristic. it is the important thing and can effected to relative soldering defects.
 
#8
Echoing Golfman… it's based on the customer needs - if you are building to their specification then they should specify which characteristics are critical to quality (CTQ) and require some sort of capability analysis.
Usually there would be such legend in drawing callout or note to specify it as like significant characteristic or critical characteristic in automotive discipline for PPAP. Some customer should have like "customer specific requirement" as part of supplier manual to follow.
 
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