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I am trying to writte a small note for our staff when they purchase components. Quite often some resistors, capacitor, inductor, diode and transistor (NPN and MOSFTET) may not be availble on the market.

For this reason swapping or replacing some components might make sense after the engineering to review those swap proposal. I have already roughly established how to replace or swap capacitor based on several criterias like this:

CAPACITOR (C)
Brand: swapable
Value (F): should be the same
Rating (V): take the same or you can take higher value
Tolerance (%): take the same or lower %
Temperature range : same or bigger range including the current range
Footprint: as to be the same otherwise can not solder on pcb
ESR: ??? (I didn't find out this)

RESISTOR (R)
Brand: Swapable
Value (Ohm): should be the same
Rating (W): take the same or you can take higher value
etc..

I am trying to establish the same format for D, L, Q, S, J

What parameters seems the more obvious for you for those 5 other components mentionned above ?

Thank you very much for your help

Neil_UK
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chris
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    Replacing even passives is fraught with risk if they are in a precision circuit: see http://electronics.stackexchange.com/questions/242648/how-reliable-is-it-to-use-another-manufacturers-datasheet-of-the-same-part/242654#242654 – Peter Smith Jul 01 '16 at 09:40
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    Personally I wouldn't leave this to purchasing - I would ask them to refer any change in component back to engineering/production for approval before placing the order. They simply don't have the technical expertise to make the judgement and if they get it wrong who would have to pick up their mistake? – JIm Dearden Jul 01 '16 at 09:44
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    Note that if a capacitor (for example) is part of a SMPS, you risk the circuit becoming unstable with a different part as it may well be part of the loop compensation; this is a task for engineering, not purchasing, as Jim Darden notes. – Peter Smith Jul 01 '16 at 09:46
  • @PeterSmith The purchasing would not choose by themselves but would suggest 2-3 parts to engineer based on availability of the part on the market – chris Jul 01 '16 at 09:50
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    Plenty of suppliers will suggest alternatives - I'm sure your buyers can forward this info to an engineer for that person to check. – Andy aka Jul 01 '16 at 09:58
  • @Andyaka I don't want to let the supplier decide but us to decide based on what we know... – chris Jul 01 '16 at 10:03
  • A very important parameter you didn't mention is the **package** type. – Curd Jul 01 '16 at 10:05
  • @Curd I mentioned it called Footprint – chris Jul 01 '16 at 10:07
  • @chris: Maybe some better interpunctation and formatting in your question would be helpful... – Curd Jul 01 '16 at 10:09
  • @chris I'm sure if you read my comment again you'll do a better job of understanding it. – Andy aka Jul 01 '16 at 10:11
  • @Curd The editor doesn't allow me to do better. I have already tried to make one line per parameters but the editor bring back all in one single line. I don't know why. – chris Jul 01 '16 at 11:01
  • @Andy aka We are based in a country where supplier interface know quite often even less than our engineer. We can not rely on them for proposal of substitution. – chris Jul 01 '16 at 11:02
  • @chris: the editor offers item lists or paragraphs (just insert an empty line) or if needed also some simple HTML formatting, e.g.
    for line break.     – Curd Jul 01 '16 at 11:05
  • ANYONE can propose a substitute. Proposing a substitute is not a problem. Accepting an incorrect sub is THE problem and it boils down to relying on YOUR engineers. – Andy aka Jul 01 '16 at 11:06
  • two spaces at the end of the line forces a new line, check my edits to your post. – Neil_UK Jul 01 '16 at 11:56

1 Answers1

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No. No.

No.

Even in the best run company, purchasing need absolutely no encouragement to come up with ways to buy stuff other than what you have specified.

Each component you use should have a list of permissible suppliers. So for capacitors for instance, 'cooking grade' applications, in the case of MLCC ones you use for PSU decoupling and signal coupling, might be available from Murata, Kemet and about a dozen other suppliers, but their permissible part numbers must be specified. High performance applications, where you need low loss, or low inductance, will have a different part number and may only be available from one or a restricted few suppliers.

Obviously if you try to do this for every component you use at once, engineering staff will be overwhelmed.

It would make sense therefore, for purchasing to report to you any difficulties they have sourcing components and have engineering staff pro-actively attempt to handle (say) 20 items a week.

Neil_UK
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