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Attrition | 8 April, 2003

I am currently trying to creat a model to calculate attrition on our SMT line. A new product is coming into our cleanroom and we have problems with the current product and atttrition levels. One of our main problems is a large batch for us (space inductry) is 13, and more often than not we are running single boards. Should i take a nominal figure for a new batch, then a percentage attrition for each part? where could i find examples of these figures? Any help appreciated, thanks for you time, chrissie

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Attrition | 9 April, 2003

What is the source of these attrited components?

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Attrition | 9 April, 2003

Probably of no help but here it is anyway

This is a tuff one. Attrition is due to many factors. You have machine rejects (visual fail, no pick), feeder set-up loss each time a reel is removed you lose X number of parts depending on feeder design (we lose 10 comps. each time we unload a 4mm pitch tape)you will lose some during reel loading. You will lose more parts during a first build while your techs are "dialing in". There is also the feeder/machine that screws up during production (assignable cause probably shouldn't be used for attrition calc.)

I would recommend that you get data from your machine as to its reject rate by package/feeder or whatever you can get. then allow for set-up/teardown loss whatever that may be.

but here is what we use for attrition when possible

discreets - 2% overage or 10 extra whichever is more Big$$ - 0% sometimes two extra in case of damage. Big parts (Dpacks, coils, etc...)- < 1% we retrieve from scrap bins and handplace

also keep in mind that when you build one assy. and the quantity of a certain component is for example, 1 per, the percentage thing obviously doesn't work (you need 10 extra parts to ensure that you do not go line down) Also make sure that all reels have adequate leader tape.


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Attrition | 10 April, 2003


Exactly what i was looking for! I spoke to the operators of the machine who said it does record the reject rate, but it hasn't been reset since the machine has been in there so that's pretty useless, although there's a couple of boards going down next week so i've asked for the data to be collected. (thankfully i'm doing a runner for two weeks to get some sun!). The other factors that you mentioned i shall now be able to research and make a good guess as to what they are in our company.

Thanks again for your help!


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