Handling Part Substitutions as a CM - Page 1
Forum section: electronics / general

author: kylehunter
author_rank: Regular Contributor
timestamp: October 17, 2023, 01:13:44 am
content: We are getting back into contract assembly work. We have an older Assembleon (Phillips) pick and place machine. In a program file it just stores the part number and footprint as identifying information. If we are running a job for a second time and there are passives that have changed to a different part number, it makes setup difficult as the pick and place is referencing a different part number than we are working with. We use partsbox for BOM management, which handles part substitutes quite well. The only real solution we have now is to manually edit the part on the pick and place to match the new part, which is time consuming and can be prone to errors.Looking forward to hearing how others manage this in their production.

author: Kean
author_rank: Unknown
timestamp: October 17, 2023, 01:30:23 am
content: Most CMs I have worked with prefer to use internal part numbers - either assigned by the client or by the CM themselves.When you check in stock, you would label all the parts with that internal part number and optionally record batch details of each run for traceability.

author: kylehunter
author_rank: Regular Contributor
timestamp: October 17, 2023, 01:32:59 am
content: Quote from: Kean on October 17, 2023, 01:30:23 amYeah I figured as much. But unless you have an internal part number that is spec based (R06030.25W120R for example, though it doesn't have to be in the name of course) and can reference multiple real part numbers, it doesn't really solve anything. Since then you'd just be assigning every new part to a new internal part.

author: Kean
author_rank: Unknown
timestamp: October 17, 2023, 01:49:27 am
content: In your example, have the passives changed value? Or just different vendor part?I gathered from your comments that it was a substitute part and thus the same value - so any generic part number is fine to cover all substitutes on the AVL. Descriptive part numbers are nice for designers and repair, but beyond goods receiving inspection they don't help that much if you are not familiar with the design.If I was running a full-time CM then I'd be assigning internal part numbers to the BOM lines, barcoding everything at goods receiving inspection, and relying on those barcodes every step of the way during production. To do it right might require some extra software to assist with validating the barcodes during PnP setup rather than human validation of semi-random numbers, but otherwise I'd expect barcodes to be easy to handle for the parts management. I actually wish I was set up this way for my prototype and small production runs.Interested to hear how others do it as well.

author: MR
author_rank: Regular Contributor
timestamp: October 17, 2023, 03:29:26 am
content: We use [part number]  [reel number]. The part number itself is always the same for the same component and new reels and that's what's mainly used for matching the reel with the program.Our software also decreases the stock number from the particular item.A single unique number has shown to be too inefficient in the past.

author: Smokey
author_rank: Super Contributor
timestamp: October 17, 2023, 08:57:37 am
content: Quote from: kylehunter on October 17, 2023, 01:32:59 amThat. And you are right, don't put the spec in the internal part number. Highly recommend keeping a spreadsheet like this.But as a CM you can't just ask your customers to change their inventory systems, so I have no idea what the right way to handle that form the CM side is.Whenever I send a kit to our CM, they audit every line item. They are overly detailed and ask tons of questions when things don't match 100% (like if I have a 5% resistor in the part description, but sent them a 1% without saying "or better"). I've learned how to tweak my systems to result in fewer questions from the CM, which saves everyone time and money.

author: SMTech
author_rank: Frequent Contributor
timestamp: October 17, 2023, 09:25:31 am
content: Internal part numbers are the answer, it helps you as a CM manage alternative parts and if you can persuade your regular customers to also adopt a similar system it makes it easier for them to pre-approve alternatives rather than doing it on a case by case and product by product basis. Ideally as a CM you would mark your incoming reels/packets with 3 bits of data - the internal part number, a goods received number/date or order number, and a reel identifier. That way if a reel has been issued and turns out to be wrong, you know which one it was and where you used it, it also helps maintain First in - First Out.There's nothing wrong with making your internal part number contain some level of part information, for things like generic resistors it can make it easier for an operative to go get some extra for rework or unexpected stock issues. It can get messy if you try and put too much info in there however and if humans are reading labels rather than scanning barcodes; semiconductor part numbers beg you to make mistakes. We use very simple part numbers like SMR 1k0 0805 and we standardise on 1% so I know without referencing elsewhere what the internal part number might be for something this generic, because it became common we add a P for 0.1% and we add a suffix for other odd variants like higher power specialised parts. A client uses a similar system but all with numbers 11-31001-08 for instance decodes to the same thing.I have definitely seen examples of people using very generic value descriptors for their component values on pick and place machines, this is fine when the reel markings also inlcude this info but plenty of brands use incomprehensible or hard to read part numbers, and it falls on its face if you have multiple different spec parts of the same nominal value. So its a bad idea unless you only build simple things and clear down the machine after every build, or chaos would ensue, and probably a bad idea even then.