Ok to re-reflow to add missing connector? - Page 1
Forum section: electronics / general

author: daloev
author_rank: Contributor
timestamp: October 20, 2022, 02:48:43 am
content: I've had very good success doing reflow at home with ChipQuik solder paste, a stencil and a toaster oven with a controller, but it can be a challenge to avoid bridging with 0.4mm pitch connectors. I have a single-sided board design with 0.4mm pitch connectors and an FMC connector. I see that JLCPCB, which I use for the boards, has the 0.4mm pitch connector in stock for PCBA, but not the FMC connector. If I get JLCPCB to assemble the board with as many parts as they have, is it ok for me to give the assembled board a pass through my own oven to add the FMC connector? I've done FMC connectors in my own oven without any problem.Because all the FMC pins are under the connector, I don't think hot air would work very well. I could try a hot plate I have, but if I am going to heat the entire board anyway, I feel more confident in my oven.

author: tomgat
author_rank: Regular Contributor
timestamp: October 20, 2022, 12:03:01 pm
content: Quote from: daloev on October 20, 2022, 02:48:43 amThe bridging issue on fine pitch components is, by far, the most common issue on reflowing. The close second is excess solder balls. You can reliably fix both by first making sure you have enough flux in your paste, and then shrinking your stencil pads for this component by at least 2 thou. Also I would suggest adding the fiducials to the stencil for easier alignment. It not only helps with alignment, but also makes for more reliable vision matching if you have a PNP machine. I also round the stencil edges too, but this is just my personal preference.Also, reflowing it is the easiest method to use for something like this. Just make sure you put a coat of flux on it before it goes back into the oven because the original reflowing burns off the flux. IMHO, its always better to have too much flux than not enough.

author: NorthGuy
author_rank: Super Contributor
timestamp: October 21, 2022, 10:10:43 pm
content: It is probably easier to send them the missing components so that they reflow all at once.

author: tooki
author_rank: Super Contributor
timestamp: October 22, 2022, 02:22:09 pm
content: Quote from: NorthGuy on October 21, 2022, 10:10:43 pmThat isn’t an option with JLCPCB. You have to either use parts from LCSC (JLCPCB’s sister company) or JLCPCB’s procurement service, which can order parts from Digikey, Mouser, Verical, Arrow, Future, and Avnet.

author: MarkR42
author_rank: Regular Contributor
timestamp: October 22, 2022, 10:19:51 pm
content: It depends entirely on what other components you have on the board. The big manufacturers have ovens which are very well temperature controlled and can reflow things such as connectors without damage.I have found that my oven does not have the same level of control. It can reflow things like ICs, passives, with no problem, but connectors or other components with plastic parts, can get too hot.Also JLCPCB seem to ignore your solder paste layer and make their own. This is not too bad, as it means they mostly don't put any paste on any pad which isn't under a part they're assembling. So ideally your boards should arrive with all the unpopulated pads nice and clean.Also, use ENIG, HASL is just not flat enough for most things and will reduce yield (not worth the saving unless your board is super cheap)

author: NorthGuy
author_rank: Super Contributor
timestamp: October 23, 2022, 02:55:22 am
content: Quote from: MarkR42 on October 22, 2022, 10:19:51 pmIt may be difficult, if not impossible, to apply paste with a stencil after other components are already in place. So, it may be necessary to use a syringe risking dispensing too much, inducing bridging. Or, it might be possible to ask them to put paste on the pads. This way, pads will be covered with the correct amount of solder. All is left is to apply flux on top and reflow. If you apply too much flux, it'll be dirty, but you won't get bridges.