Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It's 100% free.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I have made a PCB with a few minor mistakes which have been fixed by running wires around my micro on my board. This does not look great and I am hesitant to hand it over to my clients with those modifications visible.

Is it possible to create an epoxy blob around my micro at home in order to hide these modifications? Are there other alternative ways of concealing the error?

This is the type of blob that I am referring to:enter image description here to.

share|improve this question
    
Is there a reason why you can't spin another rev of the board? – Ignacio Vazquez-Abrams Jan 20 at 12:01
    
Yes i need something ready by the end of the week. the next batch of boards will contain the corrections – user3095420 Jan 20 at 12:02
6  
To be completely honest, it's not all that strange to see "bodges" in the wild even from multi-billion dollar companies that do nothing but electronic design all day, every day. – Ignacio Vazquez-Abrams Jan 20 at 12:05
    
If you posted a pic of the board maybe we could suggest ways to clean it up a bit. – George Herold Jan 20 at 14:58
    
I agree with Ignacio. I've seen hardware "patches" so discrete and well done in a comercial (well, engineering sample) board that it was just beautiful to look at it! – ricardomenzer Jan 21 at 10:49

The blob you show is from COB (chip on board) construction. The chip is not in a separate package. It is installed directly on the board, then the epoxy blob put over it, which substitutes for the chip package. This is a high volume manufacturing technique.

Yes, you can glob epoxy over most electronic things without trouble. About the only issue is heat dissipation. If the part dissipates enough heat, then you have to consider the extra thermal insulation added by the epoxy. Personally I use hot glue for most such things. It doesn't live as long as epoxy, but for prototypes that doesn't matter.

Also consider whether this really matters. Any customer that understands product development will understand that there will be multiple revs of a board, and early revs may have some manual rework. Use hot glue or epoxy to tie things down to make the reworked board mechanically rugged enough, but trying to hide rework sounds silly and probably wouldn't work anyway. A blob of expoxy or hot glue on a board for no good reason looks a lot more stupid than a little rework.

share|improve this answer
    
If heat dissipation is an issue aren't there resins (designed to go on electronics) with decent thermal conductivity? I'm sure Ive abused them in the past, and of course air can only dissipate heat through convection. – Chris H Jan 20 at 16:38
    
@ChrisH, radiation propagates heat just fine through the air as does conduction (though very slowly). – Bill Barth Jan 21 at 2:40
1  
@BillBarth radiative heat transfer is a very minor effect in typical hardware. Temperature differences are only a few tens of degrees. Unless of course you design for space applications. The TC of air is similarly very small - after all most thermal insulators are mostly air with the rest mainly to stop convection. Which is why air can only (to a good approximation) transfer heat by convection. – Chris H Jan 21 at 7:35
    
@ChrisH, yes, I'm aware. It was just your use of "only". – Bill Barth Jan 21 at 13:03

Use thin wire-wrap wire the same color as your solder mask, perhaps tack it down with a bit of epoxy here and there if the wire is very long. Strain relief or vibration resistance with hot glue, if necessary. Drill the odd hole to make the wires neater. Make any cuts neatly with a proper tool (eg. A Dremel). Plan it out and consider mounting parts a bit differently to make the rework prettier and, most important, more reliable.

Adding excessive blobs of epoxy can make the design less reliable. Any 'fixes' are going to be inherently less reliable than the rest of the board- your most important goal is to make the rework reliable enough- nobody will care how attractive it is if it quits.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.