what is the procedure regarding populating PCB`s with chips with large pin count - Page 1
Forum section: electronics / general

author: diyaudio
author_rank: Frequent Contributor
timestamp: September 30, 2015, 11:03:29 am
content: Questionwhat is the procedure regarding populating PCB`s with chips with large pin counts for small board runs, ie BGA or LQFPN what is the cost regarding pre-population for the chip only?

author: janekm
author_rank: Unknown
timestamp: September 30, 2015, 11:25:18 am
content: I presume your question is what the likely costs are for populating only the BGA or QFN parts on a board that has other components that you want to populate yourself / or leave unpopulated for a kit.The answer is of course "it depends".Firstly, there's a big difference between China and "the west". In China, even 100-unit runs are commonly placed by hand (even for reasonably large pitch BGA parts, but anything under say 0.6mm pitch BGA is better placed by machine). This keeps the setup costs much lower. If you end up needing machine assembly, you might as well get the whole board populated because most of what you'll be paying is the setup fee anyway, and there will be a minimum applied for this by any factory. For a 100-board run you are likely to end up with close to the same cost for populating 1 chip or a whole board.In "the west", a 5-board run with QFN or BGA would likely be placed on a manual machine while a 100 board run would definitely go through a full pick&place machine. Here, for the 5-board run, placing just the "tricky" part may turn out more economical.

author: zapta
author_rank: Super Contributor
timestamp: September 30, 2015, 11:34:56 am
content: You can upload your project to Macrofab and see what numbers you get.

author: MT
author_rank: Super Contributor
timestamp: September 30, 2015, 01:08:12 pm
content: Quote from: janekm on September 30, 2015, 11:25:18 am100 really? In a documentary about China being "the planets workshop" in a short section they talked about Chinese smallscale assembly fab's in this frame they showed a family on the countryside who had their own desktop micro P and P machine!The machine was no more then 1,8m by 1m, and pretty quick, the frame didnt reveille if they used mini reels or cassette!I was surprised so small P and P existed! I guess such a machine would been made specifically for e.g 100-200 board runs.

author: janekm
author_rank: Unknown
timestamp: October 01, 2015, 03:01:08 pm
content: Quote from: MT on September 30, 2015, 01:08:12 pmYes, totally. Those tiny cheap P&P machines are useless for anything needing precision, like 0.4/0.5mm pitch QFN, BGA of any sort, or 0402. I think the biggest market for the cheap, small P&P machines currently is for assembling LED light bulb PCBs (cheap LED light bulbs are a cottage industry in China currently, there's factories churning out the housings and PCBs and cottage industry for assembly).The prototype assembly house I use in China does mostly hand placement for runs up to and beyond 100 boards, and use big P&P machines for bigger runs. The setup costs for the P&P machines work out so that this is the more economical approach. You'd be amazed by how quickly a seasoned team can place 100 boards by hand. The other reason is that the big P&P machines need parts on reels, so that's even more setup work if not all the parts are on hand already on reels (yes, they'll re-reel if necessary, but of course they don't like it). You're also going to lose some parts to the machine during setup (the last two points don't apply to the same extent to high mix P&P machines like Mydata, of course, but those are not as common in China yet).

author: marshallh
author_rank: Unknown
timestamp: October 03, 2015, 03:48:12 am
content: BGA does not require much precision at all for placement. As long as you get to slightly less than half the ball pitch you're golden.QFN with thermal pad is pretty resilient.QFP with no thermal is probably the most difficult.

author: janekm
author_rank: Unknown
timestamp: October 07, 2015, 08:50:52 am
content: Quote from: marshallh on October 03, 2015, 03:48:12 amTrue enough, but the trouble with BGA is the difficulty of inspection. So 1.0mm pitch / 0.8mm pitch might be doable with a cheapo machine, but anything smaller than that I'd say you need a machine with vision and decent repeatability. Not to mention control over z-axis so the solderpaste doesn't get smooshed between pads and causes a short...Anyway, the prototyping place I mentioned usually handles anything I throw at them, but for a 0.4mm pitch BGA they complained and finally ran it through the big P&P machine