Is it bad to reflow solder paste on empty pads? - Page 1
Forum section: electronics / beginners

author: cbc02009
author_rank: Regular Contributor
timestamp: September 14, 2018, 12:00:19 pm
content: Hello all,I have a PCB I'm making for a school project. When I designed the PCB I added some optional footprints for some 1206 filter capacitors and resistors in case I decided I needed them later. Unfortunately the stencil I created has those parts in it, so if I use the stencil (without taping them off or something) those pads will get the solder paste on them. Is if safe to bake empty pads with solder paste? Will it make it impossible to install the parts if I decide I do need them? I've only every reflowed a couple breakout boards, so this is my first real reflow project.Thanks!

author: EEVblog
author_rank: Unknown
timestamp: September 14, 2018, 12:04:10 pm
content: No problem.You might have to wick off the solder later if you want to install the parts though.

author: TomS_
author_rank: Frequent Contributor
timestamp: September 23, 2018, 09:51:39 pm
content: It's very common to see production PCBs with unpopulated component positions, probably for much the same reasons you have them.Why are you thinking it would be bad?

author: cbc02009
author_rank: Regular Contributor
timestamp: September 23, 2018, 11:36:49 pm
content: Quote from: TomS_ on September 23, 2018, 09:51:39 pmI didn't think it would be, but I didn't know for sure, and you know what they say about assuming.Asking on the forum is a whole lot cheaper than screwing up a board and having to order new ones.

author: Brumby
author_rank: Unknown
timestamp: September 24, 2018, 04:47:21 am
content: Sensible.I have always said the "dumb" questions are the ones you do not ask - and you pay the price at some point.

author: Ian.M
author_rank: Super Contributor
timestamp: September 24, 2018, 05:41:54 am
content: Pad finishes other than HASL and ENIG typically have a fairly short shelf life, and even ENIG has limited shelf life due to the nickel layer oxidizing, so, reflowing the empty pads with paste at initial manufacture is likely to help maintain future solderability of all except HASL, and for HASL it does no harm.

author: LukeB
author_rank: Contributor
timestamp: September 24, 2018, 09:26:42 am
content: Sounds like a cool school project tho. Wish I could do projects like that at school.

author: TomS_
author_rank: Frequent Contributor
timestamp: September 24, 2018, 12:43:50 pm
content: Quote from: cbc02009 on September 23, 2018, 11:36:49 pmThe very reason you had put in some optional components is very much a thing. The beauty, as you thought, is that you can design them in, and simply not populate them if you can get away without them. Or maybe they arent needed for a particular version of hardware. Or maybe you want them for a later revision of hardware. Multitude of reasons, none of them bad (except taking up space, which maybe you need if you have a very compact design to achieve). Probably best to design components in and not populate them -thatmight save you from having to re-spin your boards!Heres a couple of pictures of some production boards. The first (green) one came out of some telco gear, lots of unpopulated positions there.The black one is out of an Apple keyboard. It looks like they gave themselves some options to either populate a MOSFET or a 0 ohm jumper on some kind of power rail, but in this case they seem to have gone for the 0 ohm jumper option.