Author Topic: PCB rework / jumper wires  (Read 914 times)

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Offline joris

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PCB rework / jumper wires
« on: November 30, 2017, 09:51:58 pm »
Hi All,

I found this useful guide on hot to take pcb rework to the next level:
http://www.circuitrework.com/features/630.html

http://www.circuitrework.com/guides/6-1.html
Quote
Recommended wire is solid insulated copper wire, tin lead plated, 22 to 32 AWG with Kynar [=PVDF], Milene [=PET-laminated tape?], Kapton [=Polyimide], Teflon [=PFTE] or equivalent insulation.

Does anyone how these different insulators compare especially in terms of soldering? I have a bag of "magic" #30 wire that my dad passed on to me that is amazing, while with most other wires that I recently bought the insulation instantly vaporized on first touch with the soldering iron.

I looked at temperature rating before, but I found that sometimes "high temperature wire" was worse dealing with "very high temperatures" than the normal variant.
 

Offline KL27x

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Re: PCB rework / jumper wires
« Reply #1 on: December 01, 2017, 12:16:29 pm »
Well, the way I see it:
PVC, polyesther, polyurethane are your basic inexpensive insulators. These insulations are relatively thick, and they melt/shrink well below soldering temp.

If you want an insulator that doesn't shrink, at all, the most common one I know of is Teflon or some variation of Teflon. The problem with Teflon is twofold. It is very slick. This makes it very hard to strain relieve. And it is very difficult to strip small gauge wires.

The mainstay of low current pcb-level jumperwires is Kynar insulated wire. Kynar has a very high dielectric and abrasion resistance, so the insulation can be extremely thin. This makes for less strain at the end of the wire and less bulk. It can be glued down for strain relief. And it is extremely easy to strip. It just starts to melt at lead soldering temp, which will be more noticeable on the larger gauges. For the smaller gauge, it really isn't much issue.

There are lots of peeps who seem to favor enamel insulated wire, aka "magnet wire," for fine pitch stuff. God knows why. If 30AWG kynar wire is too fat with the insulation, you are doing something that can probably be done with naked bus wire. At that level of micro rework, 30 gauge naked wire might as well be tree trunks. Just bend and arrange it to keep air gaps. I have a reel of 28 gauge magnet wire, which is significantly thinner than 30AWG kynar when you include the insulation. But it's for emergency use, only. I have never used it, lol.

 
« Last Edit: December 01, 2017, 12:32:23 pm by KL27x »
 

Offline Old Don

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Re: PCB rework / jumper wires
« Reply #2 on: December 01, 2017, 12:49:47 pm »
Kapton tape works well for an insulator.
Retired - Formerly: Navy ET, University of Buffalo Electronic Tech, Field Engineer and former laptop repair business owner
 

Online Buriedcode

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Re: PCB rework / jumper wires
« Reply #3 on: December 02, 2017, 01:12:12 am »
There are lots of peeps who seem to favor enamel insulated wire, aka "magnet wire," for fine pitch stuff.

I have used magnet wire, and whilst I prefer kynar - magnet wire with solderable insulation (as in, enamel that melts at soldering temperature) can be very quick for prototype, SMD repair, SMD proto's and last minute 'fixes' to bad layouts. No stripping required, you can tack it down, route it, and cut it to length so it sits on an IC's pin, and just solder it. Like ELMchan:

http://elm-chan.org/docs/wire/wiring_e.html

I also used a propelling pencil, a craft knife, and tweezers.  I actually haven't really done this in years, as I quickly gave up such prototyping methods in favour of cheap PCB's, and haven't done PCB repair in a while, but it can be very neat, and reasonably straight forward to repair 0.8mm pitch IC's.  I've done 0.5mm pitch before, but I wouldn't trust my repairs on those.

Kynar still looks better, and is what I used on repairs for work, just mentioning the above because I think it has its place.
 

Offline rx8pilot

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Re: PCB rework / jumper wires
« Reply #4 on: December 02, 2017, 03:49:50 am »
A few years ago I got a spool of random 30 guage solid from a local surplus house. It has been used as bodge wire ever since, but it's not fun to work with. My guess is that it's PVC or some other shrinking insulator. Now that I am down to the end of the spool....time to step up. Perhaps the Kynar is the better choice. Shrinking insulation is a pain when your bodge is close to vias and other components.

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Offline KL27x

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Re: PCB rework / jumper wires
« Reply #5 on: December 02, 2017, 09:56:29 am »
I got some of that wire when I bought a set of vintage OKI wire wrap tools on eBay. I had never seen a wrap tool like it, before, and I just had to see what the heck it was all about.

The tool was a blue pencil with a wrap bit on one end and a small spool of wire on the other. The wire ran through the body of the pencil and out the wrap bit. So it wrapped the wire backwards. (Well, at least the first wrap would be upside down; maybe you were supposed to wrap the first end with a separate tool and just finish the other side with this?). There was a small slide switch on the side which acted like a break. So if you put the brake on and wrapped a wire, it would eventually snap off the wire.

I'm pretty handy, but I never did figure out how it was supposed to work, what with the insulation still on the wire. The wire it came loaded with was 30AWG but with some kind of poly insulation, as already mentioned. If you wrapped with the insulation still on, the wire would sorta cut through the insulation and maybe-sometimes make a connection with a fat third of an inch worth of loose wrap with insulation oozing out between strands. It didn't seem to work at all with kynar. The entire kit ended up in the garbage, including the wire.

I eventually learned there is another kind of kynar wire made for CSW (cut strip wrap) bits, which cut and strip the ends, automatically. I wonder if that would have worked. I don't see where the excess insulation would have gone, though.

FWIW, this type of CSW kynar is slightly thinner but it is slicker and definitely isn't as flexible. I gave that reel away.

Quote
magnet wire with solderable insulation
I agree that would be nice to have in a pinch. But once you learn to deal with kynar, it's just easier. Unless you don't have the space for the insulation, even this stuff would be bottom drawer material for 99% of uses. It takes 0.1 seconds to flow a small 30AWG joint if you don't have to wait for insulation to melt.

r8xpilot (and OP, if you're in the US):
I have been buying my Kynar wire from eBay seller "cableall" for the last 10 years (so maybe 3 purchases of a 1000 foot reel :)). It ships from "Wes Bel" which is the same sender/dropshipper where some of my Mouser components arrive from. It's the same stuff that Radio Shack sells. I am very particular about my bodge wire. I've occasionally tried to save money by buying from Hong Kong or China, and it wasn't the same stuff.

So with a 1000 foot reel of the green stuff I treat like it's free, and a small roll or another color which I use like it's gold (for, say, twisted pairs or for indicating one end of a connector), I'm pretty much set. I just cut off an arms length or so, what is easy to manage, get er done, and throw away any leftover. Great for making making custom cables with pin header, getting signals to logic analyzer, and the like, too. I also primarily use this kind of wire for breadboarding, sticking pinheaders into the board and wrapping the connections. When done with the breadboarded circuit, it all just goes into the bin. I don't have a lot use for reusable jumpers. Another example is if I want to connect my DMM to ground, temporarily. More often than not, I don't have a place to put an alligator or mini clip that is secure. I have a banana plug with a square section filed in the top. I just wrap the end of a piece of kynar around the square post and solder the other end to the board. When I'm done, the kynar immediately gets ripped off and goes into the bin, and the special banana plug gets snapped back into the holder that is glued to my meter. Life is too short, and kynar is too cheap. :) I have a 1000 foot roll dispenser/cutter permanently mounted to the right of my hot air within arms reach. It's a consumable as much as a component. Probably more than half of this wire I buy ends up in the bin.
« Last Edit: December 02, 2017, 11:44:38 am by KL27x »
 

Offline Kilo Tango

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Re: PCB rework / jumper wires
« Reply #6 on: December 02, 2017, 11:02:24 am »
Perhaps it was a Verowire pen. The wire has insulation that melted around solder's melting point, so you wrapped it around the component legs, put a blob of solder on your iron, and held it to the joint. When it got hot enough the solder would flow and make the joint.

Once upon a time we used to wire up 40 pin Processors, 28 pin Eproms and 8 off 16 pin Dram chips with these things. And they worked ...... sometimes !

Ken
 

Offline KL27x

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Re: PCB rework / jumper wires
« Reply #7 on: December 02, 2017, 11:14:55 am »
Thanks! I googled Verowire Pen, and I got a couple different pics. The main difference is the blue OKI pens (set of 4; I feel kind of bad decommissioning them, lol) was that they had a wrap bit in the tip where the wire came out.

I suppose it might have just been Verowire Pen PLUS (plus also an awkward wrap bit).

The wire that it came with certainly melted at soldering temp, but it appeared to be ordinary pvc or polyurethane wire to me.
 


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