Author Topic: Tinning traces for more current  (Read 19512 times)

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Online mikeselectricstuff

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Re: Tinning traces for more current
« Reply #25 on: July 19, 2012, 10:53:05 am »
Chemtronics Soder-wick (dispite the misspelling!), Iron is a Metcal
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Online mikeselectricstuff

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Re: Tinning traces for more current
« Reply #26 on: July 19, 2012, 11:25:16 am »
Is the 'normal' track there going to struggle with 1A? I would have thought it would have done ok, what happens at higher current?
You can work it out - I^2*R = 26 milliwatts dissipated at 1 amp, so negligible. On a PSU it will be more about reducing voltage drop  - there are lots more heat sources on a PSU to worry about before track heating becomes a major issue.
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Offline HackedFridgeMagnet

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Re: Tinning traces for more current
« Reply #27 on: July 19, 2012, 11:42:33 am »
@mikeselectricstuff
I assume that is 1oz copper on that board, is that correct?
And it was pb/sn that you removed.
 

Offline Poe

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Re: Tinning traces for more current
« Reply #28 on: July 19, 2012, 07:36:16 pm »
Thank you mike.  It definitely looks effective. 

Although I wonder what kind of solder that was.  There appears to be a significant conductivity range between solder types based on this chart from Indium:
http://www.microwaves101.com/encyclopedia/SolderChart.cfm#chart

2% to 23% = 4x to 50x the resistance of copper?  Is that right?

If the 4x stuff was removed and the 50x stuff added, the gain would be negligible.  Other way round and the gain substantial.  Does anyone know of 'typical' solders used in production environments today (pb-free types) and their conductivity range? 

You might need to to define a solder type in your assembly documentation if the range is large.

Mike,
Not to be a pedantic bother, but could you apply 60/40 so we have a base for comparison?
« Last Edit: July 20, 2012, 04:23:24 am by Poe »
 

Offline EEVblog

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Re: Tinning traces for more current
« Reply #29 on: July 20, 2012, 02:15:23 am »
I just shot a video on this. Will upload in due course.
I was able to get better results than Mike.

Dave.
 

Offline Poe

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Re: Tinning traces for more current
« Reply #30 on: July 20, 2012, 04:24:21 am »
I just shot a video on this. Will upload in due course.
I was able to get better results than Mike.

Dave.

...ya, but he was first!

 ;D

Thank you.
 

Offline EEVblog

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Re: Tinning traces for more current
« Reply #31 on: July 20, 2012, 05:04:12 am »
...ya, but he was first!

But I did it the proper way!  :P

Dave.
 

Online mikeselectricstuff

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Re: Tinning traces for more current
« Reply #32 on: July 20, 2012, 11:44:39 am »
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Offline G7PSK

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Re: Tinning traces for more current
« Reply #33 on: July 20, 2012, 05:40:16 pm »
I just found a length of non cored solder left behind by the plumber. 200mm X 3mm dia. measures 0.53 ohms on my meters using croc clips for connection.
 

Offline robrenz

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Re: Tinning traces for more current
« Reply #34 on: July 20, 2012, 05:53:03 pm »
Matweb data

60/40 solder Electrical resistivity 0.00001499 ohm-cm
http://www.matweb.com/search/datasheet.aspx?matguid=06a31d97bb734b509043d81cf131b280&ckck=1

Oxygen-free high conductivity Copper, Soft, UNS C10200  Electrical Resistivity  0.00000169 - 0.00000173 ohm-cm
http://www.matweb.com/search/DataSheet.aspx?MatGUID=9aebe83845c04c1db5126fada6f76f7e

60/40 solder is 8.76 times more resistive

Offline amspire

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Re: Tinning traces for more current
« Reply #35 on: July 21, 2012, 12:31:33 am »
Mike,

In your thermal test, it looks like the track with the solder had the heat spread much more evenly. That should mean that the soldered track has a better ability to loose heat via air conduction and radiation, but the shiny solder is probably radiates less heat then the coated track.

So overall, the end result is probably very similar.

It would be interesting to know how the coated copper track compared to the tinned track if you wick up most of the solder. Does a thinly tinned track get noticeably hotter then the masked track?

The risk with relying on the wave soldering to deposit solder on the track is that to get a thick layer of solder, the track has to be parallel to the solder wave. If the assembler puts the board through the wave soldering with the track at right angles to the wave, the thickness of the tinning will be much less.

Richard.
 

Offline EEMarc

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Re: Tinning traces for more current
« Reply #36 on: July 21, 2012, 03:27:49 pm »
For serious current capability, solder copper wire or precut copper foil or sheet to the unmasked traces on the PCB. You can achieve anywhere from a few oz to well over 100 oz copper traces on demand this way.

Sometimes having 400+ amps and fine pitch components on the same board is a nice thing to be able to do.
 

Offline ampdoctor

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Re: Tinning traces for more current
« Reply #37 on: July 21, 2012, 04:17:32 pm »
For serious current capability, solder copper wire or precut copper foil or sheet to the unmasked traces on the PCB. You can achieve anywhere from a few oz to well over 100 oz copper traces on demand this way.

Sometimes having 400+ amps and fine pitch components on the same board is a nice thing to be able to do.

I've seen this done a number of times on higher quality power supplies.  They just take a section of 18awg solid wire and snake it around where they need it.  Down side here is that it has to increase the production time and labor costs substantially. So I would think this would be best left to where you need some really high current capacity in a limited amount of space, or the price bump won't have any significant effect on the profit margin.  Anywhere 5 bucks can be a deal breaker on a final product, I can see where just tinning a trace would be the preferred solution.
 

Offline G7PSK

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Re: Tinning traces for more current
« Reply #38 on: July 21, 2012, 06:17:21 pm »
I have just found that the new set of croc clips I got have a bad crimp joint and that is where the high resitance came in my measurement of solder.
I soldered the solder to the meter leads and got 0.1 ohms per meter with 3mm dia solid solder, no flux cores.
 

Offline Bloch

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Re: Tinning traces for more current
« Reply #39 on: July 21, 2012, 06:54:38 pm »
I have just found that the new set of croc clips I got have a bad crimp joint
The hours i have lost over the years to bad test leads  :-[
The first thing i do with new croc clips test leads is solder the "crimp" before use.
 

Offline ejeffrey

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Re: Tinning traces for more current
« Reply #40 on: July 21, 2012, 07:08:59 pm »
I have just found that the new set of croc clips I got have a bad crimp joint and that is where the high resitance came in my measurement of solder.
I soldered the solder to the meter leads and got 0.1 ohms per meter with 3mm dia solid solder, no flux cores.

That is better, but still not quite there.  You need to do a 4 wire measurement to test this accurately.  Incidentally if you were doing a 4-wire measurement the bad crimp wouldn't have corrupted your measurement.  3 mm of lead-free solder should be about 0.02 ohm/meter.
 

Offline codeboy2k

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Re: Tinning traces for more current
« Reply #41 on: July 23, 2012, 06:08:54 am »
For serious current capability, solder copper wire or precut copper foil or sheet to the unmasked traces on the PCB. You can achieve anywhere from a few oz to well over 100 oz copper traces on demand this way.

Sometimes having 400+ amps and fine pitch components on the same board is a nice thing to be able to do.

I've seen this done a number of times on higher quality power supplies.  They just take a section of 18awg solid wire and snake it around where they need it.  Down side here is that it has to increase the production time and labor costs substantially. So I would think this would be best left to where you need some really high current capacity in a limited amount of space, or the price bump won't have any significant effect on the profit margin.  Anywhere 5 bucks can be a deal breaker on a final product, I can see where just tinning a trace would be the preferred solution.

wouldn't it be possible during manufacturing to mask off the board and electroplate extra ounces of copper on traces that needed high current carrying capabilities.

sometimes the board is done with a tin resist and electroplating to build up a 1/2-oz copper blank into a 1-oz copper board.
Something like this...

1.    Drill all of the holes in a 1/2 oz. copper coated board.
2.    Electroless copper coat to activate the vias.
3.    Electroplate enough to stabilize the vias.
4.    Mask the board to expose only the areas to be saved.
5.    Electroplate 1/2 oz. of copper.
6.    Electroplate tin.
7.    Strip resist mask.
8.    Etch in ammonium persulphate.
9.    Strip the tin resist
10.  Apply solder mask
11.  Dip in solder for HASL

new steps 4 and 5 (and extra steps in between)
4.   Mask the board to expose only high current traces
4.1 Electroplate 3 oz of copper
4.2 Strip the resist mask
4.3 Mask the board to expose all the traces to be saved, including high current traces
4.4 Electroplate 1/2 oz of copper
5    Electroplate tin

At this point, the board has 1 oz of copper everywhere, and 4 oz of copper on high current traces, and TIN resist everywhere.

I don't know if this would work. There might be severe undercutting on the 4oz copper areas, or maybe manufacturing processes wouldn't allow for the extra steps.  The PCB designer would need to create an extra mask.

This is not "free" like the exposed soldermask, but is also not extra work during assembly like snaking wire or soldering copper foil or straps.

 

Offline EEMarc

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Re: Tinning traces for more current
« Reply #42 on: July 23, 2012, 09:18:10 am »
I like the way you think codeboy2k.

I have no idea if that would work though since I've never done plating.
 

Offline SeanB

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Re: Tinning traces for more current
« Reply #43 on: July 23, 2012, 03:52:31 pm »
Can be done, but will add signifigant cost to the board for very little gain. You would be better off to have a laser cut copper foil and place it on the board with solder paste and then IR reflow it.

If you need the high current tracks then you will use the 2 or 4oz copper and add a mezzanine board with the fine pitch components.

Otherwise you will add a copper wire to the board, or use solderwick and solder it to the appropriate places.
 

Offline codeboy2k

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Re: Tinning traces for more current
« Reply #44 on: July 23, 2012, 11:08:57 pm »
Can be done, but will add signifigant cost to the board for very little gain. You would be better off to have a laser cut copper foil and place it on the board with solder paste and then IR reflow it.

If you need the high current tracks then you will use the 2 or 4oz copper and add a mezzanine board with the fine pitch components.

Otherwise you will add a copper wire to the board, or use solderwick and solder it to the appropriate places.

Yeah these ways are certainly way cheaper.  I like the idea of a mezzanine board of 1oz copper on top of a or beside a 2oz or 4oz board., or reflow a copper foil trace on top of existing traces that need a current upgrade.
 

Online tom66

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Re: Tinning traces for more current
« Reply #45 on: July 24, 2012, 07:56:25 am »
Now here's something interesting from an LG LCD TV power supply. Ignoring the rather scorched MOSFET for now the one thing that is apparent is that they've tinned the traces, but they've done diagonal stripes on larger planes. Also, the pitch seems to be different on the output side. Why?
« Last Edit: July 24, 2012, 08:03:55 am by tom66 »
 

Online digsys

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Re: Tinning traces for more current
« Reply #46 on: July 24, 2012, 12:04:31 pm »
I'm pretty sure it's because their "fattening" method is so poorly thought through, that it'd create HUGE blobs on larger
surface areas. I've seen it on earlier REALLY cheap P/Supplies. I've had cases of 1 in 5 failing, and upon opening them up
found huge dangly blobs just shy of the case. I think the method they use is melting the solder in a WOK and flinging it
on to the PCB. Having many narrow tracks limits this effect.
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Offline Poe

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Re: Tinning traces for more current
« Reply #47 on: July 24, 2012, 02:30:10 pm »
Thank you mike.  It definitely looks effective. 

Although I wonder what kind of solder that was.  There appears to be a significant conductivity range between solder types based on this chart from Indium:
http://www.microwaves101.com/encyclopedia/SolderChart.cfm#chart

2% to 23% = 4x to 50x the resistance of copper?  Is that right?

If the 4x stuff was removed and the 50x stuff added, the gain would be negligible.  Other way round and the gain substantial.  Does anyone know of 'typical' solders used in production environments today (pb-free types) and their conductivity range? 

You might need to to define a solder type in your assembly documentation if the range is large.

Mike,
Not to be a pedantic bother, but could you apply 60/40 so we have a base for comparison?

Just got word back from our factory.  We commonly use Cookson make SAC-305 for Pb-free assemblies.  It is 44% more conductive than 60/40.  The other Pb-free alloy we run which has "better performance" has 52% less conductivity.  On Pb assemblies we use 63/37 which obviously is just a tad more conductive than 60/40.

Based on alloy alone, the parallel conductivity could vary three fold!

Since thickness is a crap-shoot, maybe it's a good idea to verify the conductivity of your assembler's alloy when using this technique?

Oh ya...
The SAC-305 conductivity is 16.6% IACS
99Pb/1Cu 12.6% IACS  (similar to Dave's latest video)
63/37 is 11.9% IACS
60/40 is 11.5% IACS
MX alloy is 5.5% IACS

Copper obviously >100% IACS
 

Offline SeanB

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Re: Tinning traces for more current
« Reply #48 on: July 24, 2012, 03:37:43 pm »
WRT the LG PCB I guess that these are panelised, and can go through the wave bath either way, so the diagonal is the best compromise. The design is probably rotated so that a maximum number of mixed boards for that model will fit on a single larger panel.
 


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