Parts management of Caps by EIA classification

[ewinter]

I am a experienced component engineer that has worked at my current company for 7 months. It is a medical device company. On our "AVL" we have a part # that is described as follows: AVL CAP,0.1UF,50V,Z5U,0805
This particular device configuration is at the high end of the capacitive range for 50V and 0805,etc. The question of adding an X7R component was raised because of the perception of a "BETTER" part. Now it it is true to say the dielectric properties will provide more stable characteristics over temperature, a 0.1UF,50V,X7R,0805 will be physically thicker and is considered at the top of the available capacitive value for this configuration and some manufacturers do not manufacturer this configuration as a standard part. I have proposed several options that include creating a new part number for the X7R and considering a lower voltage part, etc.
In my experience this is a relatively simple issue to deal with. An X7R is not a Z5U and should not be mixed on the AVL or on a product particularily since the part is of a thickness that concerns me AND we have seen cracking of these capacitor in our application so I would certainly want to AT LEAST manage the traceability of the change and application.
What are you thoughts?

 

[IRstuff]

I guess the big question is why you're finding resistance to that concept. Given that the temperature and other physical characteristics are different, the parts are NOT interchangeable.

If the circuit is designed for the more stable part and the less stable part is used, the circuit may fail or operate outside of spec over temperature.

Additionally, if you're using pick and place for assembly, there may be issues if the part is not exactly identical, since the machine may place the part incorrectly and the board traces may not be compatible, causing tombstoning or other problems.

TTFN

 

[ewinter]

It is more like refusal. In past lives this wouldnt even be a question.
I guess being in a medical device these things arent improtant (that was sarcasm if you didnt notice)

Thanks for your response. it serves as a sanity check for me.

 

[IRstuff]

Try throwing "product liability" around. Maybe that'll get their attention. ;-)

TTFN

 

[designchain]

Yes...that'll get their attention!

Interchangeability is the keyword. Once you set the precedence of allowing your AML to be polluted because what is viewed as a secondary component property is irrelevant to one design, you will live to regret it.

Mike

--
Mike Kirschner
Design Chain Associates, LLC

http://www.designchainassociates.com