Manufacturers for standard parts in BOM? - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: July 13, 2021, 03:18:07 pm
content: Supposing you have parts like SMBJ20A, 1N4148, BC847, UC3842, chip resistors and capacitors, etc etc, which are made by many different manufacturers, ….is it safe to put “ANY Manufacturer” in the Manufacturer column of the BOM? (so that the Board stuffer/whoever, can more easily and cheaply source the parts without constantly sending emails saying “will this be ok…?”Actually, we would put (“Any manufacturer except Multicomp”)

author: Siwastaja
author_rank: Super Contributor
timestamp: July 13, 2021, 03:54:29 pm
content: Works fine for non-critical designs requiring no approvals regarding exact component choices. But as always, work with your CM about specifics. With low-cost Chinese CMs, counterfeit/no-name substitutions are a real problemevenwhen specified with exact part number, so allowing them to choose any makes their life really easy, but that doesn't necessarily translate into lower price, but in current times of component shortages, solves lead time problems since some random Chinese substitute is always available. They avoid completely nonfunctional fakes because customer would ask to redo the boards.Don't send gazillion of emails "will this be ok", finalize your BOM first and ask what they have and about their sourcing practices in one go. In my experience, CMs don't want to spend a lot of time talking about their practices in general; they want your files. As soon as you submit as finalized file set as possible, you get feedback what to change.It really depends, with some CMs large part of their business is sourcing, with others, they want you to either ship components or give exact part numbers / order codes.

author: MarkR42
author_rank: Regular Contributor
timestamp: July 13, 2021, 09:34:22 pm
content: I've started just putting the required spec of the component e.g. 1k resistor 0603 5% - because I know the cheap manufacturers might substitute it anyway and it avoids me looking up the exact part number and them doing the same and swapping for a generic part. I've done this a few times for resistors, caps and led and it seems ok. This is not very critical though, I'd want to speicfy the manufacturer for anything really active and important.

author: TimFox
author_rank: Super Contributor
timestamp: July 13, 2021, 10:41:54 pm
content: I once collaborated on a switching power supply design, where I chose a particular tantalum capacitor that had lower-than-typical ESR. On the first prototype, the output ripple was too high, because the other engineer's BOM stated only the capacitance and voltage rating, without the manufacturer and part number I specified, and the second party to the project stuffed a normal capacitor. When troubleshooting the prototype, I quickly noticed that the body color of the SMD tantalum was wrong, compared with that of the desired manufacturer.

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: July 14, 2021, 12:32:53 am
content: Whereever possible, I refer to a real standard. Like, for example BS EN 140401-801..804 for regular SMT resistors. There are more of them than one might suspect. And you can weaken it up again by wordings like 'or equivalent' which leaves much open, but still sets a framework regarding the set of parameters which can be incomplete, but not entirely omitted.Of course I am part of an industry, where most component entries are followed by 'established reliability' etc. and where the use of 'or equivalent' happens very responsibly for the most part, such as allowing the contractor to use the series of components which are designed for, but not qualified according to the relevant MIl- or CECC or younameit-standard. If you look closely at the major and specialist manufacturers offers, there is such a series along every fully qualified one.Also, brevity should not be overdone. For example, there is no reason to omit wattage of a resistor just because you specified SMT size. Technology, value, tolerance, power, TC and max. voltage should be in a minimum spec. Also, a footnote in the BOM should reference the sizes to IEC, JEDEC, EN, or IPC.Beyond that, especially in the commercial domain where quality is still sought but pennies are counted, it does pay really well to invest some time in a component selection guideline. There you can elaborate on the parameters above by, for example, calling up a test standard or setting tolerances for the secondary parameters too.Also, you can name distinct manufacturers and product series which do not come under a standard.(for example, give them a cercap series or two from AVX, Kemet, TDK, Vishay and Murata and they will need a very good reason to deviate from this)Further, this is the place where you can hone the 'or equivalent' expression into something usable, if youspecify that- selected equivalents must undergo a qualified datasheet crosscheck by the contractor- manufacturers other than listed must have a QMS system in place- datasheets shall have their values referenced to normals and/or shall state uncertaintiesAs this is work that you will do only ONCE it will become a very powerful tool over time. And a lot of this work can be contributed by someone from purchasing or the team secretary. Industry and regulator standards can find their way into that but you can also name components or companies which work well and which you want to be used without further explanation.When you just think about it for a day, you will have countless entries. Like having coax connectors crimped or soldered and not 'stuck on', which surface treatment you like to have on your mounting hardware or not, that structural composites need to fulfill UL 94 V-0 as minimum and so on. Then come test and inspection and labels and markings and that the produced objects must be accompanied by their test reports in whatever form you agree on and and and...Then you stipulate adherence to this document in your contracts and Bob is your uncle.Of course, some quirky parameter can always lead to unexpected consequences, but this should keep the worst shit away from your products. And you can use it to achieve selective results. You could push towards use of leading edge components or keep a manufacturer (and your designers) deliberately away from them.

author: Feynman
author_rank: Regular Contributor
timestamp: July 17, 2021, 08:17:19 am
content: We always specify full part numbers. But our BOM has a "DESC" field that says something like "1n MLCC, 10% 50V X7R 0402". Additionally we have a "ALT" column that says "any with equivalent attributes (see DESC)". We do this for jelly bean chip capacitors and chip resistors. If we really need a specific part number because of more strict requirements (e. g. a capacitor with lower than usual ESR) we simply leave the ALT column empty or enter full part number an manufacturer of an approved alternative.