Optimize for Mass Production, Q regarding enclosure end panels and switch/jacks - Page 1
Forum section: electronics / projects

author: frank26080115
author_rank: Regular Contributor
timestamp: December 19, 2012, 05:07:44 am
content: I am designing something that is supposed to be portable and hand held, with a few switches on it, an audio jack, maybe a DC barrel jack, maybe a rotary encoder.I think I want to use an off-the-shelf plastic enclosure with the removable end panels, drill holes into the end panels for the jacks and switches and things.The components usually have several options, and I've listed my questions about each optionright angled mounted on PCB, and with or without threads, I just drill a hole into the end panel at the exact right spotin a mass production scenario, how can the soldering be so precise that every hole lines up with the component perfectly? or am I supposed to make the holes slightly larger to account for this?what if I am a perfectionist and demand that a component must be dead center vertically in the panel but the component's height is too short? I can see using risers/standoffs/washers on the PCB but what if that is not an option due to other constraints? Use panel mounted components instead?Or... panel mounted with threads, I screw it into the end panel, and have to somehow wire the component into the PCB afteris this economical or efficient? there will be an extra step involved, soldering wires to the component, and then soldering it to the PCB, or another connector which plugs into the PCB, these sound like time consuming steps involving manual labour. can this be automated?should all of these components connect to the circuit board via soldering directly or use an another connector since the connector can probably be pick-n-placedIt's a product that should have enough volume to justify not building it in my own house, but not enough volume to have it built by Foxconn.

author: TerraHertz
author_rank: Super Contributor
timestamp: December 19, 2012, 08:40:02 am
content: Quote from: frank26080115 on December 19, 2012, 05:07:44 amGet it laser or water jet cut - more accurate and nicer cuts.QuoteIf you use threaded items that need manual addition of nuts, etc on the end panels, you'll really add to the labor costs. Depending on the connector and switch type, it's better if you can avoid making the end panel and pcb 'one assembly' by screwing them together via connectors, switches, etc.QuoteMany connector types have some of their solder-pins made with <> style springs, so they will self-center in appropriately sized PCB holes.Components that don't, if you want accurate positioning you have to get the final plated and tinned through holes size just right. You want the part to drop in easily during pick and place, but have very little free play. Buy a micrometer gauge, get some actual samples of the parts you'll use, measure the pin size 'max radius' (diagonally across rectangular pins, etc.) Ask your intended PCB manufacturer for info on their hole plating and tinning options and tolerances. Don't try to get it too close - it's very annoying for the PCB assembler to have to bash parts into holes with a hammer.QuoteToo many variables to answer. Your choice.QuoteIf you want to multiply the assembly cost by some large number, sure.QuoteYou should be asking prospective manufacturers this. They'll have relative scales for manual work vs automated PCB assembly.

author: Niklas
author_rank: Frequent Contributor
timestamp: December 19, 2012, 10:17:46 am
content: I think I have seen some products where small connectors and buttons are not physically fixed to the panel itself. Instead, they are firmly fixed to the PCB and may use the panel just as a support and limiter against excessive bending etc. The drawback is that those components must be through hole mounted instead of surface mounted, i e extra soldering step in the production. The components that you listed should be possible to find in through hole mount packages.One of the most common failing connectors I have seen lately is the surface mini USB with those tiny soldering pads. Now you can find a good alternative that is through hole mounted that can withstand a lot of bending before and pad rips off the board.I don't have the exact number, but I would not be surprised if the mechanical tolerances of the board contour and the drilled component pads have a placement tolerance of about 0.1 mm. The hole to hole distance tolerance is probably a bit better, at least for plated holes, than the hole to board outline tolerance. Plated holed (pads, vias), unplated holes (large screw holes) and board contour are all made at different manufacturing stages, unplated holes and routing might be in the same step, and all steps have its own board alignment error.

author: frank26080115
author_rank: Regular Contributor
timestamp: December 19, 2012, 05:25:19 pm
content: QuoteDefinitely an option, I think.QuoteYou mean those huge things on the side of a DB9 connector? I don't think I'll have any of those though.QuoteSoldering by hand is very different from reflow or wave soldering, with the automated soldering, does solder have a tendency of self-centering the component? I know for SMD reflow, pads usually self-centers.QuoteYeah, well I trust the PCB manufacture to not to screw up enough to cause the design to absolutely fail. The holes in the plastic box will probably be about 0.3mm larger than what they need to be, does that number sound good?QuoteMy preferred USB connector is a through hole micro-B connector but it seems like the legs are more meant for super thin PCBs, like 0.8mm. If I wanted to use such a connector on 1.6 mm PCB, can I just have the same hole but cover that hole in the solder paste layer?Thanks for the answers guysedit: I fixed the nested quoting