Pages: [1] 2   Go Down
Author Topic: Tacking wires to PCB - How?  (Read 1368 times)
0 Members and 1 Guest are viewing this topic.
Manchester, New Hampshire
Offline Offline
Edison Member
*
Karma: 4
Posts: 1363
Propmaker
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I'm having some boards made, and the assembly house needs to do some rework on them that involves adding a couple wires to the bottom of the board.  The end user is likely to apply double sided tape to the bottom of the board however and I am concerned about the wires pulling loose if they decide to pull the board off whatever they've stuck it to. 

Currently, I use jumper wires for breadboards to make these repairs.  They're pretty sturdy.  But I assume the board house has their own wire and it's easier/cheaper to use that than to have them cut up jumpers as I did. 

I asked the board house if they adhere the wires to the board in any way and they said they don't, but that they're flexible and can do whatever I want.

The problem is... I don't know what I want.  Or rather, I have no idea what sorts of adhesives or tape or whatever would be typically used for this sort of repair.  Digikey sells some adhesives but I have no idea what the right one would be.  Kapton tape springs to mind.  I think I've seen that used but I have never used it and don't know how strong it is.

I suppose I could just tell them to tack the wires in place using superglue but that doesn't seem like what the professionals would do.

So, any suggestions?   
Logged

AL
Offline Offline
Newbie
*
Karma: 0
Posts: 32
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

You could use a low temp glue gun.
Logged

Manchester, New Hampshire
Offline Offline
Edison Member
*
Karma: 4
Posts: 1363
Propmaker
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Hot glue would make a mess of the board.  I've used it in the past where I attached wires for battery terminals to a board to prevent them from flexing to the point that they break.  I found epoxy works a lot better for that.  But it takes time to dry and the mixing nozzles quickly get clogged up.   
Logged

UK
Offline Offline
Shannon Member
****
Karma: 223
Posts: 12630
-
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Is there any way to swerve the issue by routing the wire so that it avoids the flat areas where users are likely to try to stick things onto the board, or is protected by other components on the board?

If not, perhaps you could put a not-very-sticky sticker on the board that covers the vulnerable areas and prevents anything from adhering to the wire. You were looking for somewhere to put that "warranty void if removed" sticker, weren't you?
Logged

I only provide help via the forum - please do not contact me for private consultancy.

UK
Offline Offline
Tesla Member
***
Karma: 135
Posts: 7680
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Perhaps you could add a protective base below the wires so that the user has something proper to put their sticky pads onto. But I've no idea whether a small piece of plastic would blow your budget.

...R
Logged

Manchester, New Hampshire
Offline Offline
Edison Member
*
Karma: 4
Posts: 1363
Propmaker
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I'm going to be making the repairs myself after all.  The manufacturer wanted $10 per board to attach a couple wires (a job which takes me all of two minutes) and they didn't offer any suggestions for how to bond them to the pcb.
Logged

South UK
Offline Offline
God Member
*****
Karma: 5
Posts: 585
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

http://uk.rs-online.com/web/p/conformal-coatings/3217324/

We always use the above to secure reworks to our PCB's. It seems to work well for securing fine wires and also SMD resistors if we only have one pad to solder to etc.
Logged

Southeast US
Offline Offline
God Member
*****
Karma: 15
Posts: 683
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I'm a big fan of the hot glue gun way of doing this rework.  Unless you are trying to tack down the entire length, I usually put a blob that covers the wire every 3" (Or one in the middle if less).  Otherwise I would get the big jars of 5 minute epoxy and mix it yourself, and do all the boards at once.  You definitely need to tack down those wires though, or they will break after a while.

I like the Acrylic too, how viscous is it?

Edit: On further thought, you could probably use superglue if you can make sure the wires are pressed against the PCB so there isn't any gap.
« Last Edit: September 26, 2013, 10:52:55 am by mirith » Logged

South UK
Offline Offline
God Member
*****
Karma: 5
Posts: 585
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset


I like the Acrylic too, how viscous is it?


It's hard to say, personally i think its perfect - small blobs don't spread too far, and the more you apply the further the spread. If that makes sense! I have used this method lots of times, we coat all our PCB's in acrylic conformal coating (same as the bottle but in aerosol format) but any reworks get protected with the bottled stuff first. I use it on loads of other projects for securing things - even seems to work well for strain relief on cables - I use a lot of ribbon cables that don't usually last long if moved about.

in the photo below you can just about see it on the kynar wire and the 0805 resistors on the back of the LCD module to the left

Logged

Manchester, New Hampshire
Offline Offline
Edison Member
*
Karma: 4
Posts: 1363
Propmaker
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

The problem with hot glue is it's often hard to get the tip of the glue gun in close enough to the wires you need to tack.  Also, in this instance, the blobs of hot glue would make the underside of the PCB very uneven, and the user needs to be able to mount it on a flat surface with double sided foam tape. 

Luckilly, I'm going to do the job myself so I don't need to worry about it anymore.  I'll be using breadboard jumper wires, and those are sturdy enough for this to be a non-issue.

This is what it looks like when I do it myself:


The kynar wire and acrylic is an interesting solution though.  If the route the wire had to take were more convoluted I might go for that.  But these jumpers are really convenient and fairly inexpensive.
Logged

Global Moderator
Boston area, metrowest
Offline Offline
Brattain Member
*****
Karma: 545
Posts: 27353
Author of "Arduino for Teens". Available for Design & Build services. Now with Unlimited Eagle board sizes!
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Looks sharp.
I have to put a wire on a tqfn pin, not going to be nearly as pretty!
Logged

Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

Manchester, New Hampshire
Offline Offline
Edison Member
*
Karma: 4
Posts: 1363
Propmaker
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I was lucky to have broken out USART1 for serial debugging.  Those wires are an SPI bus for my LED drivers which were on the same bus as my DAC.  Unfortunately it turned out I could not send data to only one or the other and there was insufficient time between sound samples to update the leds.
Logged

Manchester (England England)
Online Online
Brattain Member
*****
Karma: 634
Posts: 34528
Solder is electric glue
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

At many places I have worked in electronics we have used this:-
http://uk.rs-online.com/web/p/surface-mount-silicone-adhesives/1987144/

or this

http://uk.rs-online.com/web/p/surface-mount-silicone-adhesives/0473398/?origin=PSF_435906|alt
Logged

Offline Offline
Newbie
*
Karma: 0
Posts: 10
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

conformal coating is also excellent for sealing the entire board once a project is "complete" and requires no further enhancement. it's ideal for ever-changing climates where the board is somewhat exposed to the elements of things like condensation within the cabin of a motor vehicle. a lot, if not all OEM's use these type of coatings on their ECU/ECM/PCM to prevent short circuits from things like moisture attacking the PCB, and it needs removed if one wishes to modify the board! very good products indeed.
Logged

South UK
Offline Offline
God Member
*****
Karma: 5
Posts: 585
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

conformal coating is also excellent for sealing the entire board once a project is "complete" and requires no further enhancement. it's ideal for ever-changing climates where the board is somewhat exposed to the elements of things like condensation within the cabin of a motor vehicle. a lot, if not all OEM's use these type of coatings on their ECU/ECM/PCM to prevent short circuits from things like moisture attacking the PCB, and it needs removed if one wishes to modify the board! very good products indeed.

Pretty much why we use it on our automotive products. The worst thing about it is trying to seal up the connectors when coating using spray. We tried many but found acrylic to be the easiest to use, you can solder through it and it just melts away and then apply more over the reworked area with the brush. It's also easy to remove using IPA in a ultrasonic bath.
Logged

Pages: [1] 2   Go Up
Jump to: