PCB connector problem - Page 1
Forum section: electronics / projects

author: sirhaggis
author_rank: Regular Contributor
timestamp: July 10, 2016, 12:34:08 pm
content: Hi all,I am designing a project with some unconventional problems relating to connectors. I have PCB board which has multiple connection points (a dozen or so but potentially up to 20-30), where each connection point may use some of a set of high speed digital signal and power lines (25 or so). What is actually connected to each connection point is something that is customized after the fact, so the board is a generic design without presetting what lines are available at each connector site. The generic board is then customized with modular plug-ins at each of the connection sites (where each module uses some subset of the available lines). My problem is finding a cost effective and durable solution that allows many such connection points without driving the cost of the board up excessively. Each module site will need to be able to access any of the lines but may actually only use a handful of them. Therefore I need a connector solution in which I can place up to 30 connectors onto the PCB, each with 25+ connection points that a module can access. Even stacking cheap pin headers in this situation seems to be cost prohibitive once you get to 25 points over 20-30 connectors.I thought of a couple of potential solutions for this but none so far seem spectacular... I could place low cost fine pitch mezzanine connectors at each connector point (with 30 or so contacts) which would come in at around <$1 per connection - however the most durable connector I have found so far comes in at 50 mating cycles which is within the realm of reason but I would really like to get 100+ cycles for the application. I also thought about having simple exposed pads on the PCB and using pogo pins on the modules to contact only the required pads - this would make the PCB cheap, but unfortunately pogo pins seem excessively expensive and would make the modules too expensive if they use more than a few pads.Does anybody have any other ideas?Thanks for your timeLuke

author: Ian.M
author_rank: Super Contributor
timestamp: July 10, 2016, 01:10:03 pm
content: How fast are the digital signals?What's the max power rail voltage and current per module?One option you probably hadn't considered is an anisotropic conductive elastomer sheet between ENIG pads on both the module and motherboard. Seehttp://test-probe.jp/en/product/anisotropic_conductive_rubber/acr_-_gold_plated_gold_wire_type_matrix_series.htmlYou'll probably need a clamping bar and a backing bar with two fixing screws per module to get even contact pressure, unless you get washers cut from the anisotropic elastomer sheet, and arrange the contacts in a ring round each fixing screw, which would then go directly into a threaded insert on the motherboard.

author: sirhaggis
author_rank: Regular Contributor
timestamp: July 10, 2016, 01:27:16 pm
content: The signals will be up to 30MHz, there will be 3.3V and 5V rail (both fairly low current). There may be a 12V rail for higher current modules but that is yet to be determined.Thanks for the link, I have not seem this product before, will definitely look into it..

author: MosherIV
author_rank: Super Contributor
timestamp: July 10, 2016, 04:05:47 pm
content: HiHave you looked at the old connectors used for VME bus?132 connections, still available and not terribly expensive.

author: sirhaggis
author_rank: Regular Contributor
timestamp: July 10, 2016, 04:17:58 pm
content: "Have you looked at the old connectors used for VME bus?"Good idea, but unfortunately the spacing requirements mean that whatever connector I use has to fit in an area of about 1 inch by 1 inch.

author: sirhaggis
author_rank: Regular Contributor
timestamp: July 10, 2016, 04:30:48 pm
content: "One option you probably hadn't considered is an anisotropic conductive elastomer sheet between ENIG pads on both the module and motherboard"Regarding this solution, do you know where I could read up on these materials and their application in circuits? The Tespro site you reference provides very little in the way of specifications or application information and I am not familiar with it at all. Having done a little bit of Googling, I'm not sure where to start if I wanted to prototype with it, as it doesn't seem to be an item sold by many outlets in small quantities... or one on which there is a great deal of information readily available (at least where I was looking)

author: Ian.M
author_rank: Super Contributor
timestamp: July 10, 2016, 05:03:26 pm
content: http://www.fujipoly.com/usa/design-guidelines/91.htmlI've got no idea where to get small quantities of the elastomer sheet type other than by requesting samples. 3M's self adhesive anisotropic conductive tape is in common use all over the maker movement but I haven't seen anyone retailing the non-adhesive elastomer version.