PCB Pitch error - Page 1
Forum section: electronics / projects

author: pyrohaz
author_rank: Regular Contributor
timestamp: July 29, 2014, 08:04:09 am
content: Hi all,I've designed a PCB with a section of pads at a pitch of 1.27mm to fit a ribbon cable. After seeing how hard it was to strip a ribbon cable and solder it to these sockets without the strands going everywhere/melding into one conglomerate of solder mess, i'm wanting to use an FFC cable instead. On many cheap Asian products, I see the FFC soldered directly to the PCB and this seems a pretty easy way to achieve connectivity. After a bit of searching, I couldn't seem to find FFC cables with a pitch if 1.27mm, I could however find them with a pitch of 1.25mm.I've got 6 pads (to use with 6 way ribbon cable initially) with 1.27mm spacing. If I was to use an FFC cable with this 1.27mm spacing, I'd incur and error of 0.12mm (1.27x6 - 1.25x6) which to me seems minimal. Could anyone give me a bit of light on this situation?Cheers,

author: pyrohaz
author_rank: Regular Contributor
timestamp: July 29, 2014, 08:11:07 am
content: For reference:http://uk.rs-online.com/web/p/flat-ribbon-cable/4682628/This is the kind of cable I'm talking about.

author: Ribster
author_rank: Frequent Contributor
timestamp: July 29, 2014, 08:17:11 am
content: I'm not sure if my URL will pass through in a good fashion, but i did a quick parametric search on digikey and could select the option of .1" and .05" spacing for FCC.http://www.digikey.com/product-search/en?FV=fff40019%2Cfff80232%2C1640002&mnonly=0&newproducts=0&ColumnSort=1000011&page=1&stock=0&pbfree=0&rohs=0&quantity=&ptm=0&fid=0&pageSize=25Search the commonly known chinese vendors / ebay and you'll find a perfect solution.

author: pyrohaz
author_rank: Regular Contributor
timestamp: July 29, 2014, 08:33:48 am
content: Quote from: Ribster on July 29, 2014, 08:17:11 amHey, cheers for the link! I've searched on digikey and found one that suits my needs (A9AAT-0608E-ND) but I find it really hard to justify the £12 postage charge! Do they only post from USA? I'm not intending to spend over £50 so I find it really hard to justify the expense.I've tried searching ebay (worldwide) for both 1.27mm FFC and 0.05" FFC with no luck on results, there are trillions if I search 1mm of 0.5mm pitches.

author: johnwa
author_rank: Frequent Contributor
timestamp: July 29, 2014, 08:52:12 am
content: Quote from: pyrohaz on July 29, 2014, 08:04:09 amIf you get the alignment nominally correct in the middle, you should have an error of only +/- 0.06mm at each end.

author: Ribster
author_rank: Frequent Contributor
timestamp: July 29, 2014, 08:55:23 am
content: Like johnwa said, bodge it on if it's a prototype.If else, try aliexpress.com they maybe have something..

author: pyrohaz
author_rank: Regular Contributor
timestamp: July 29, 2014, 09:10:36 am
content: Quote from: johnwa on July 29, 2014, 08:52:12 amWhen you put it that way, it seems a bit less of a deal! I'll buy one off RS and see if it fits alright. I was hoping to have this as a final PCB revision though I suppose it would be better engineering to do it correctly! When it comes to PCB assembly, can assemblers attach FFC cables on one end?Quote from: Ribster on July 29, 2014, 08:55:23 amI've been looking to buy off aliexpress actually! Would you recommend it? I buy a fair few asian electronic components off ebay and they're all pretty good quality normally.

author: Ribster
author_rank: Frequent Contributor
timestamp: July 29, 2014, 09:50:56 am
content: Quote from: pyrohaz on July 29, 2014, 09:10:36 amI've been buying stuff from ali for almost 2 years now. What can i say, it's cheap, from china and takes long :p.I feel quite safe to buy from ali, because in the rare occasion that i have had issues, i always got my money back. A few times with the dispute system.Just don't let yourself be pushed around, and if it's really cheap then there is always a reason for it.The most common reason will be the shipping, so expect very slow delivery/no tracking for very cheap things. And reputation of the seller is a big deal to me.