Need help evaluating PCB assembly options - Page 1
Forum section: electronics / general

author: DaveHardy
author_rank: Regular Contributor
timestamp: October 26, 2017, 07:03:21 pm
content: I've got a small circuit board I've been stuffing by hand, and I'm thinking about having it assembled professionally. I've got a few questions I'd like some feedback on before I consider my first run.1.) I'm assuming SMD is a lot cheaper than through hole assembly?2.) How do you approach boards that need large heat sinks mounted?3.) I'm really worried about Chinese fab houses using counterfeit / inferior parts. Should I get boards made in China and have them assembled here?4.) How do I compare cost and rates of different fab houses?5.) What are common mistakes that I should avoid?

author: rea5245
author_rank: Frequent Contributor
timestamp: October 26, 2017, 08:12:08 pm
content: Regarding questions 1 and 4,PCBShopper.comdoes price comparisons of PCB assembly (in addition to it's better-known comparison of manufacturing). Enter information about the number and type of your components, and PCBShopper will show you assembly prices from up to 9 well-known companies in Asia and the US. Note that the prices do not include the cost of components (which is presumably the same no matter who you have do your assembly) or the price of fabricating the PCBs.Disclosure: I run PCBShopper.- Bob Alexander

author: DaveHardy
author_rank: Regular Contributor
timestamp: October 26, 2017, 10:13:20 pm
content: Thanks! That's a helpful service!

author: zeqing
author_rank: Regular Contributor
timestamp: October 27, 2017, 07:45:34 am
content: 1.) I'm assuming SMD is a lot cheaper than through hole assembly?--> yes, the SMD pads cheaper, especially in mass production.2.) How do you approach boards that need large heat sinks mounted?-->now quite understand, the "heat sink" can be installed on the PCB by screws normaly.3.) I'm really worried about Chinese fab houses using counterfeit / inferior parts. Should I get boards made in China and have them assembled here?--> have a prototyping around to try and see how the vendor works.4.) How do I compare cost and rates of different fab houses?--> send your production related files to candidate vendors, to compare the price. of course, the price should not be the only aspects for you to select the the fab hourse.Personally i suggest you the makerfabsservice@makerfabs.com, they will let you know every components price and the brand will be used, and the price good, quality OK.

author: Kean
author_rank: Unknown
timestamp: October 27, 2017, 12:10:04 pm
content: Some comments regarding Q4 & Q5 based on past experiencea) Make sure when comparing assembly quotes, that they're for the same thing. I've had a client proceed with a cheaper quote (without discussing with me) and it turned out that component cost wasn't included. In the end the cheaper quote was slightly more expensive (but not by much).b) Be aware of the MOQ cost on components sourced by the assembly house. While assemblers will typically have stock of common "jellybean" parts, they will also try get you really good bulk pricing on anything they don't stock as it makes the quote look more attractive per unit cost. What they don't always tell you upfront (often in the "fine print") is that you'll be responsible for paying for the full MOQ of the bulk purchases. I've seen this as high as $2,000 extra on a $10,000 order. Those excess components will be returned to you if you don't place another assembly order that will use them within a couple of months. If they're for export (e.g from China) they will often they'll be stored in a "bonded warehouse" as the duty hasn't been paid on them, and thus there is a deadline on exporting them.c) Be aware of lead times. Again to get per unit costs down, they'll try find the best prices on components, but that may push lead times out by weeks if not months.Re Q3, if assembling in China you need to work with a trusted manufacturer that sources components from trusted supply chain (e.g. Digikey). You tell them this upfront when getting the quote, and tell them you'll need documentation to prove it, and you'll be doing cross checks of batch numbers. It is a little tricky to enforce, but it has worked for me. Having someone on the ground who can visit the factory is very useful here. Generally the supply chain tracking it is only needed on the more costly or specialty parts. You can always supply the parts yourself, but this is painful when importing to China (very strict customs) and a dodgy company could still swap out the good parts you supply with cheaper, then resell yours.Q1 is almost always yes, and for Q2 it is unclear what you mean.

author: Ice-Tea
author_rank: Super Contributor
timestamp: October 27, 2017, 03:11:27 pm
content: Quote from: DaveHardy on October 26, 2017, 07:03:21 pmIn general: yes. There are exceptions, but no need to worry about that now.QuoteDefine 'big'?QuoteUnless you're running insane volumes: have them stuffed local or local-is. If you're running insane volumes: be prepared to put some work in a good dossier or forget about it.QuoteAs with all things: as a number of quotes. Make sure to always ask for the same thing. Compare.QuoteThinking "No need to write this down, I'm sure they know this kind of stuff".

author: DaveHardy
author_rank: Regular Contributor
timestamp: October 31, 2017, 02:28:02 am
content: Thanks for all of the insight guys.I'm not sure what the next logical step should be for me.I've got a couple of expensive op amps and some expensive resistors on my board. I don't really know what else could get the old switcheroo by the Chinese besides caps and regulators.. Price for board stuffing in USA is a lot more expensive, but it would eliminate some variables for me. Maybe I should get them assembled here?Parts cost me around $50 each when making this board and takes 2 hours of my time to assemble each if I do runs of 10 at a time. A run of 100 would cost me about $35. I was thinking about switching to SMD, getting rid of the To-220 heat sinks and using the board to dissipate heat. Maybe I should try a run of 100? How would you guys assemble these with heat sinks, hardware and all to get the most bang for your buck?Here's a picture of my board and dimensions are about 100 X 200mm.

author: Ice-Tea
author_rank: Super Contributor
timestamp: October 31, 2017, 07:09:06 am
content: That's a lot of TH... May be worth it to make it SMD as much as possible, especially if you want to have it done locally...

author: DerekG
author_rank: Frequent Contributor
timestamp: October 31, 2017, 11:51:27 pm
content: Quote from: DaveHardy on October 31, 2017, 02:28:02 amIf those TO-220 devices are running hot, you will never be able to put them directly on the board to dissipate the required amount of heat (well you might if you add a fan). If they are mosfets, can you locate a lower Rds part so they dissipate less heat? Yes, they will cost more, but they will generate less heat.

author: zeqing
author_rank: Regular Contributor
timestamp: November 20, 2017, 10:31:06 am
content: 100 pcs batch with THT would be a little more expensive, for the for 1,000 pcs, the soldering cost will double , or even triple. use the SMD components if you think the project will be larger...as the heat of Mosfet, it is meaningless to discuss if you need to change it, higher price, better quantity with lower heat; just select the cheapest solution that can meet the requests.

author: IconicPCB
author_rank: Super Contributor
timestamp: November 20, 2017, 07:36:16 pm
content: As already noted...materials will not alleviate the need to dissipate power.Optimal solution use SMD for bulk of components select high power packages that will provide performance irrespective of technology involved.You could consider SMD repackaged to dissipate the power through the use of some of the modern heat spreader materials.I have seen compliant putty like compounds which flow around the components when compressed in order to enhance heat flow into a flat heat sink,Think of Your finished assembly as a sandwich structure of PCB thermal blanket and a flat heat sink base.

author: KL27x
author_rank: Super Contributor
timestamp: November 21, 2017, 07:57:20 pm
content: QuoteThis is like asking if you should buy comprehensive car insurance (well, assuming you actually own the car, rather than making payment to the bank to use their car, it is your choice). This would depend on the car, your neighborhood, your personal financial situation, and your tolerance for risk.I know this may sound strange, but it is possible to send your own parts to china, too. When I started out, I used a local company which I would provide them parts, and they would ship them to China. If this sounds inefficient, well, what can I say. They've been in business for over a decade, and they're still open. The price wasn't terrible.One potential option to explore is to examine which of your parts are very expensive and critical. If it's only a very small percentage of the board which you might worry about, you might consider removing those from the cream/paste layer and just tacking those on, yourself.

author: miceuz
author_rank: Frequent Contributor
timestamp: November 21, 2017, 09:51:12 pm
content: I am usinghttps://makerfabs.com- they are relatively new fab-less shop, but people working there have loads of experience and speak English very well. I will base my answers on my experience with these guys (I have tried Itead, Seeed and Elecrow before)Quote from: DaveHardy on October 26, 2017, 07:03:21 pmYes, SMD pad is 3ct, through hole is 4ct (in 500-1k pcs orders YMMV)Quote from: DaveHardy on October 26, 2017, 07:03:21 pmThey can do manual work after SMD/THT assemby also - cleaning, screwing, packing, testing, etcQuote from: DaveHardy on October 26, 2017, 07:03:21 pmIn the quotations they specify which parts are going to be sourced locally and which will be used as per your BOM. You can always comment/work on that. Sometimes there is no point to use exactly the same 10k resistor. Sometimes local connectors are good enough and cost 10x less.Quote from: DaveHardy on October 26, 2017, 07:03:21 pmSend you manufacturing set (gerbers, BOM, schematics, placement file, assembly drawing, picture) to different manufacturers?Quote from: DaveHardy on October 26, 2017, 07:03:21 pmDon't underestimate importance of all of the manufacturing set documents. I have reused a footprint for RGB led once, there was no 1pin marking on it. Then I have reused 3d model from different part. Boards came with leds soldered in wrong orientation and it was only myself to blame - they used 3d rendering to determine the orientation of leds as there was no marking on silkscreen. Pay attention to provide all the information in consistent and clear form.

author: zeqing
author_rank: Regular Contributor
timestamp: November 24, 2017, 02:05:32 am
content: Quote from: KL27x on November 21, 2017, 07:57:20 pm+1. send the components that you think risky to the assembly house, but note to declare the value<800$ to avoid custom problem, and use the UPS or Fedex, avoid to use the USPS... your packages are almost lost when you hand them to USPS for shipping to China.

author: zeqing
author_rank: Regular Contributor
timestamp: November 24, 2017, 02:17:22 am
content: Quote from: Kean on October 27, 2017, 12:10:04 pmYes, but if producing in China, the digikey/mouser would be not the best candidate vendor, some common components such as resisotor/capacitor/connector price double, or even triple, compares their local price.Quote from: Kean on October 27, 2017, 12:10:04 pmAbout the shipping to China, i have so much experience and never got lost after the failing of the first time...1. <800$; 2 . use the Fedex/UPS, but not DHL/USPS

author: miceuz
author_rank: Frequent Contributor
timestamp: November 28, 2017, 07:26:30 pm
content: Sometimes it is cheaper to buy components here and ship them to China via "gray" channels than buy components in China. Again - it is a matter of talking to your manufacturer - they have various ways of importing stuff to China on the cheap - ship them to Hong Kong, declare different price, different contents, etc.

author: zeqing
author_rank: Regular Contributor
timestamp: November 29, 2017, 09:39:34 am
content: Quote from: miceuz on November 28, 2017, 07:26:30 pmIt's a really secret tip