EEVblog #317 - PCB Tinning Myth Busting

[EEVblog]

Dave.

[David_AVD]

I wonder if the standard HASL process during bare board manufacture would measurably decrease the track resistance compared to masked?

[george graves]

So basically, you're adding a resistor(the solder, lets call that R2) in parallel to the copper (lets call that R1) - and so that will always *decreases* resistance.  No matter how big R2 is.



Duh!  I'm a noob and even I knew that 

Now the question I have is that if you could magically separate that solder from the copper, and measure it's resistance, would it add up?  Or is there an interaction between each little segment of copper, and each little segment of solder happening to further lower the resistance?

[huseyinkara028]

I am wondering,
Is it possible for either copper or solder can crack due to heat and expansion by the length?
More clearly we have two different materials on top of each other and they have different thermal properties. The amount of current they carry probably different and the heat be produced by this current will be different. Due to this heat they will expand ( I know small amount) and apply opposite forces to each other. Is that possible to be the trace crack  due to this reason? Have you folks see this kind of stuff before?

Thanks.

[Electr0nicus]

That would be very unlikely. You are right that different materials expand differently, but solder is a very soft alloy, so cracks would be relatively rare. Further reading about thermal expansion http://en.wikipedia.org/wiki/Thermal_expansion

[arcoshpl]

I thought about the same Problem like huseyinkara028.

I think in long term there can be an issue. Tin has a two times bigger expansion coefficient. When a device heat up thousand times in his live the resisters will increase because of minimal cracks in the material. I don't think that you will find something like this in high quality devices.

Arcosh

[robrenz]

Wtih Tin/Lead alloy and Copper all being very ductile/malleable I don't think you will see cracks from difference in themal coeficient of expansion ever.

ductility http://en.wikipedia.org/wiki/Ductility

[David_AVD]

Over many years and many many circuit boards in equipment seen for service, I can't say I've ever seen cracking in the solder mass areas.

The cracking is always on joints that had insufficient solder to start with or were subjected to high heat stresses.  Never on thickened traces though.

[arcoshpl]

I mean no visual cracks.

More something like this.

http://en.wikipedia.org/wiki/Grain_boundary

But I think it is a normal process that also in normal soldering point happens.

Arcosh

[digsys]

Same here, rarely ever seen the solder separate from the Cu.
The junction where the 2 metals meet (1 metal and 1 "compound") forms a sort of new valence bonding.
ie at that point, you have a new alloy, after all, the metals chosen in the solder are selected EXACTLY for that
purpose. Alloy junctions can have weird properties, DIFFERENT to the base metals. It's kinda a voodoo science.
SO to answer a previous question, IF you separated the Cu and Solder and calculated resistance separately,
it would differ slightly to them combined because that junction has different properties.
Mixing different metals together to find new and often strange properties is an awesome field. Some of my
colleges have spent 20-30 yrs playing with that shit.

[Stephen Hill]

Dave,

Would you be willing to test the actual current capacity of a soldered and unsoldered trace by slowly increasing the current until the trace lifts/breaks?

In theory ohm's law should hold true that if you half the resistance you can double the current. I'm curious if the real world matches the theory.

Cheers
Stephen

[robrenz]

Daves measurements from before (1.001A & .05249V = .05096 Ohm) and after solder removal (1.004A & .05249V = .05228 Ohm) give a 2.59% increase in resistance with the minimal solder film still on.  Is there an alloying effect going on increasing the resistance or is this just measurement variations?   (or did I make some math errors? )

[dda]

Daves measurements from before (1.001A & .05249V = .05096 Ohm) and after solder removal (1.004A & .05249V = .05228 Ohm) give a 2.59% increase in resistance with the minimal solder film still on.  Is there an alloying effect going on increasing the resistance or is this just measurement variations?   (or did I make some math errors? )

It would have been good to weigh the Cu board and Cu+solder boards to see how much was still there after removal. Need a 5 or 6 figure balance.

[EEVblog]

Daves measurements from before (1.001A & .05249V = .05096 Ohm) and after solder removal (1.004A & .05249V = .05228 Ohm) give a 2.59% increase in resistance with the minimal solder film still on.  Is there an alloying effect going on increasing the resistance or is this just measurement variations?   (or did I make some math errors? )

I can only presume that some copper leeches out during the wicking process.
The setup seemed too stable and repeatable for that to be within the margin of error.

Dave.

[Monkeh]

I think it's pretty clear that you can rely on getting 15% or so improvement in current capacity with this method. Which is pretty good as a safety margin. Just helps find that little extra breathing room on a PCB.

[Psi]

It's really only good for adding extra safety margin to your existing margins.

But that's still quite useful, especially when free.

[mikeselectricstuff]

Daves measurements from before (1.001A & .05249V = .05096 Ohm) and after solder removal (1.004A & .05249V = .05228 Ohm) give a 2.59% increase in resistance with the minimal solder film still on.  Is there an alloying effect going on increasing the resistance or is this just measurement variations?   (or did I make some math errors? )

The solder does form an amalgam with copper at the surface - my metallurgical knowledge isn't up to knowing how the conductivity of amalgams relates to the constituent metals. As Dave mentioned, scraping of copper during unsoldering may also be an issue - whouldn't be hard to test that

[Rufus]

I can only presume that some copper leeches out during the wicking process.

If solder didn't dissolve copper they wouldn't need to iron plate soldering iron bits and Muliticore would never have made Savbit solder which already contains 2% copper.

On the vid shame you didn't attempt to measure the thickness of added solder - didn't you get some callipers free the other week? If whichever solder has 10 times the bulk resistance of copper then adding 10 times the thickness of solder will halve the track resistance.

On Dave vs. Mike competition I get the impression Mike wants to know the answer and the video is a bonus, Dave wants to make a video and the answer is a bonus

[GK]

Just for general trivia, never tin plate tracks carring heavy RF current with the idea of reducing track resistance. The skin effect will only ensure that the current largely flows in the lesser-conducting tin plating, thus actually raising the track resistance. This actually becomes significant at frequencies lower than what some might imagine. But then again if you are designing high power RF amps (just for example) you probably know this anyway.

[nitro2k01]

GK, for the same reason, would it make sense to route multiple parallel traces instead of a big solid single one, similar in spirit to Litz wire, or do you run into other problems if you do that?

[EEVblog]

On Dave vs. Mike competition I get the impression Mike wants to know the answer and the video is a bonus, Dave wants to make a video and the answer is a bonus

How do you figure?
I went to more trouble to get additional results.
If I just wanted a video I could have just wicked off some solder quick and dirty like Mike did 

Quick lead free video shot this morning. Sorry, no measuring of actual thicknesses etc.

Dave.

[croyleje]

I am not exactly sure how the flux is applied in wave soldering if anyone knows I would like to know but I think that using rosin core solder like Dave did would have some marginal effect on the copper itself.  Rosin being a organic acid is going to attack the copper just as it does any oxidation on the board and at only 35 microns it wouldnt take much to change the trace.

[amspire]

I am not exactly sure how the flux is applied in wave soldering if anyone knows I would like to know but I think that using rosin core solder like Dave did would have some marginal effect on the copper itself.  Rosin being a organic acid is going to attack the copper just as it does any oxidation on the board and at only 35 microns it wouldnt take much to change the trace.

The board first gets flux applied, then passes on to the wave.

The wave is just solder - nothing else. To stop oxidation of the solder, there is a thin film of oil over the top of the solder, but it is inert - it does not act as a flux. Any solder oxides float on top of the solder and they get scraped off from the wave.

[IanB]

Would be interesting to see a comparison with a length of copper wire laid on the trace and soldered down, or a length of copper wire soldered through hole as a jumper instead of the trace.

[Rufus]

On Dave vs. Mike competition I get the impression Mike wants to know the answer and the video is a bonus, Dave wants to make a video and the answer is a bonus

How do you figure?

For example you spend about 1:30 talking about 4 wire measurement and more a bit later, Mike covered it in about 20 seconds.

Mike documents what he did and the results with the video. You spend more time explaining why and how you did which is for the sake of the video.

Showing what you did is required to understand the results, talking about why and how doesn't get better or faster results.

I am not critical of either approach just commenting on the difference.

[digsys]

For all high current PCBs, I use minimum 3+3oz, most of the time 4+4oz, Top and bottom.
Then leave the solder mask exposed for 80% of the Cu strip, makes a HUGE difference
with heat !! Also allows me to Solder a thick wire the full length for heavier currents.
I add two "stake" holes at each end in case I need to do it. This set up easily carries 20A
with very little Cu heating. PLUS, I always add a two isolated ~3" strips along an edge
for testing, one exposed, and one masked. It verifies the quality of the PCB.

[Ed.Kloonk]

On Dave vs. Mike competition I get the impression Mike wants to know the answer and the video is a bonus, Dave wants to make a video and the answer is a bonus

How do you figure?

For example you spend about 1:30 talking about 4 wire measurement and more a bit later, Mike covered it in about 20 seconds.

Mike documents what he did and the results with the video. You spend more time explaining why and how you did which is for the sake of the video.

Showing what you did is required to understand the results, talking about why and how doesn't get better or faster results.

I am not critical of either approach just commenting on the difference.

The difference to me is the 90 seconds to explain that is all good stuff to a knuckle dragger such as myself. It's a slipery slope if we were to ask Dave to tell the "cut to the chase" viewers to, in fact, cut to the chase. I've been sitting here today with a bottle of plonk, playing catch up after a long week. I've enjoyed watching the videos up until this time.

There is one thing I noticed though, there is some long black pole leaning up against the bench on Dave's right. Wondering if this is some personal security instrument that Dave keeps in case of surprise ninjas or something..


 

[EEVblog]

For example you spend about 1:30 talking about 4 wire measurement and more a bit later, Mike covered it in about 20 seconds.
Mike documents what he did and the results with the video. You spend more time explaining why and how you did which is for the sake of the video.
Showing what you did is required to understand the results, talking about why and how doesn't get better or faster results.
I am not critical of either approach just commenting on the difference.

I like talking about the how and why, much to the disgust of the 3 minute attention span viewers 
I think it's what makes my videos personable, but as always, YMMV vary as the viewer. It's not a deliberate choice I make for the sake of "better video", it's just my natural style.

Dave.

[rohitdesa]

You'll notice (and I think Dave pointed it out too) that the solder on the board shown in the video (not the vero board, the other one) was no really consistent. It was narrower to the left. An interesting technique that manufacturers use to get more consistent results is to have multiple thinner un-soldermasked on the PCB track. The image will explain it better. Its from an old UPS I have. Visible on the top is a track with multiple parallel unmasked lines. And on the bottom are traces where the woule trace is unmasked.

I suppose the thicker unmasked areas are less consistent because during wave soldering the solder collects in globs and the weight of the glob is more than the force of adhesion to the copper, so the liquid solder falls off. With multiple narrower unmasked zones, you'd obviously have to have a wider overall trace if the same lower resistance is required, but it would be more repeatable.

[SeanB]

Older soldermask would have wrinkling on large surfaces of tinned copper, so that is often why there were multiple tracks and crosshatched ground planes.

[digsys]

GK, for the same reason, would it make sense to route multiple parallel traces instead of a big solid single one, similar in spirit to Litz wire, or do you run into other problems if you do that?

In all honesty I have no idea. Can't say that I've ever seen that done either.

Being flat and thin, a copper trace is already better suited for skin effect, we wind HF S/Mode Inductors with copper ribbon.
Having lots of thinner tracks is a waste of area and has no remedial value.

[siliconmix]

is heating the copper twice or three times going to anneal the copper somewhat and change it's resistance ? .just a a thought

[free_electron]

I like talking about the how and why,

Keep that up ! That is the true educational aspect. Blindly repeating things is for monkeys. The web is already full if mind-numbingly dumb copycats of copycats of badly copied of parts-reduced becasue their function was misunderstood designs.

[ejeffrey]

is heating the copper twice or three times going to anneal the copper somewhat and change it's resistance ? .just a a thought

Not much.  Technically it makes some improvement but unless your copper is very badly work hardened it won't make any difference.  Heating is more likely to change the conductivity through oxidation, and possibly chemical reactions involving any impurities in the copper.

[siliconmix]

maybe ejeffrey .here's an excellent url on the subject
http://pcdandf.blogspot.co.uk/2012/03/keepin-it-smooth-how-surface-roughness.html

[ejeffrey]

Thats for RF.  Surface roughness has zero impact on DC/low frequency losses.

[siliconmix]

 to get an accurate measurement both samples must be the same .the same ambient temperature.same meters .

[McMonster]

I saw Dave's Twitter entry about Polish subtitles to this video so I wanted to check it. It's mostly correct and acceptable, but I've spotted a few errors and disparities. Also it omits completely some important parts of what Dave actually says.

Is there a way I can edit or submit my corrections? Can't see any option like this in the YouTube interface.

[SgtRock]

Greetings EEVBees:

--Now maybe Dave can do an experiment to confirm whether or not the light in the fridge goes out when you shut the door. Just kidding. Excellent video. I finally learned how to do a four wire resistance measurment. Bonus!

"Wish in on hand and whiz in the other, and see which one fills up first."
Gator Dundee 1948 -

Best Regards
Clear Ether

[EEVblog]

I saw Dave's Twitter entry about Polish subtitles to this video so I wanted to check it. It's mostly correct and acceptable, but I've spotted a few errors and disparities. Also it omits completely some important parts of what Dave actually says.
Is there a way I can edit or submit my corrections? Can't see any option like this in the YouTube interface.

Yes, you can download the subtitles from here:
http://www.universalsubtitles.org/pl/videos/UzjoXbTCkgld/info/eevblog-317-pcb-tinning-myth-busting/
No idea how to edit them.
I can re-upload (no one else has the access), but herein lies the problem with this subtitle business - how am I to know which one is more accurate?
You may have spotted a few errors and disparities, but how do I know which one is actually better?
Who do I trust? 

Dave.

[Monkeh]

Who do I trust? 

Dave.

Whichever one speaks English the most fluently. Assuming they're translating to their native language, anyway. If they can't string together a simple sentence without errors, they can't translate worth a crap, either.

[Rick]

Who do I trust? 

Dave.

Whichever one speaks English the most fluently. Assuming they're translating to their native language, anyway. If they can't string together a simple sentence without errors, they can't translate worth a crap, either.

Not true. The guy may have perfect command of English but may not speak Polish in the same way or he may be unable to translate into Polish properly. Say someone born in USA or UK for example. Ask them to translate a test of 200 words. You will know. That's how they do.

[Monkeh]

Who do I trust? 

Dave.

Whichever one speaks English the most fluently. Assuming they're translating to their native language, anyway. If they can't string together a simple sentence without errors, they can't translate worth a crap, either.

Not true. The guy may have perfect command of English but may not speak Polish in the same way or he may be unable to translate into Polish properly. Say someone born in USA or UK for example. Ask them to translate a test of 200 words. You will know. That's how they do.

Please read my post again. I did address that.

[Rick]

Yeah that's right. As I told you, they may think they speak Polish properly but may be they are not. But I made a mistake about the test. You get them translated into Polish then you need a translation back into English (but this time the translator needs to be a confirmed one). If your sentences changed then you know who is wrong. They do those back translations a lot especially the agencies who do not master the target language.

Speaking English and translating into Polish is an entirely different business. Even speaking Polish and translating into Polish is an entirely different business. Speaking does not mean being able to translate.

[Monkeh]

Yeah that's right. As I told you, they may think they speak Polish properly but may be they are not.

If it's their native language I should hope they can speak it properly.

Speaking English and translating into Polish is an entirely different business. Even speaking Polish and translating into Polish is an entirely different business. Speaking does not mean being able to translate.

If you can speak both languages fluently you should be pretty capable of translating between the two.

I do believe I've just hit your language barrier.

[Rick]

Sure you must think you are always right. I am doing this to earn my life (not from English) so may be I know something about it.
Even if you speak both languages fluently you cannot always translate from one to the other, ask any translator he will tell you.

[Monkeh]

Sure you must think you are always right. I am doing this to earn my life (not from English) so may be I know something about it.

No, I just think you're misinterpreting what I've said. And your English seems to confirm that. So, let's try again: If you can't speak English properly, what chance do you have of translating it into any other language?

Even if you speak both languages fluently you cannot always translate from one to the other, ask any translator he will tell you.

Perhaps not, but if you can't speak one of them properly, then you certainly can't translate from it!

[McMonster]

There's a relatively simple solution that yelds good results, peer review. I'll put my corrected version somewhere on the forum for the other people speaking Polish to give their opinions. Yes, I'm aware of the confidence problems in this area, but this way of thinking can ultimately lead only to abandoning any translations at all.

And from my experience translating to one's native language is much simpler, English has the advantage that it is so widely know and simple that a lot of people (especially working in technical fields, like me) can't even try to avoid it.

[EEVblog]

Someone from the Polish electronics forum http://www.elektroda.pl did the first translation.
They are talking about doing some others as well.
I'm happy to upload any attempted translations, but peer reviewed ones are always better of course.
You can't obtain better results than when nerds fight it out  %-B 

Dave.

[McMonster]

I once considered translating your videos more regularly as you post them, but this was more or less at the time when you started doing feature length electronics movies as your blog entries. But if someone helped me this could actually be a good idea.

[Rick]

Sure you must think you are always right. I am doing this to earn my life (not from English) so may be I know something about it.

No, I just think you're misinterpreting what I've said. And your English seems to confirm that. So, let's try again: If you can't speak English properly, what chance do you have of translating it into any other language?

Yes it is a necessary condition but I am saying it is not sufficient. Because you seemed to hint that Dave should chose the better speaking one: "Whichever one speaks English the most fluently." Does that make sense?

[Monkeh]

Sure you must think you are always right. I am doing this to earn my life (not from English) so may be I know something about it.

No, I just think you're misinterpreting what I've said. And your English seems to confirm that. So, let's try again: If you can't speak English properly, what chance do you have of translating it into any other language?

Yes it is a necessary condition but I am saying it is not sufficient. Because you seemed to hint that Dave should chose the better speaking one: "Whichever one speaks English the most fluently." Does that make sense?

Yes. Why? Because it's not only logical, but it's the only thing he can compare.

[And!]

The easiest way to improve my translation is:
-download the srt file
-create your account on universalsubtitles
-re-edit it in online tools universalsubtitles

I am aware that the translation maybe is not perfect,
I took all the important elements covered in the video,
some details may have missed, maybe something can be improved.
->McMonster, If you can upgrade the translation I would be happy with it  .
I will confirm this fact here.

I confirm, there is a plan making the translation of the videos on elektroda.pl.
We'll see what comes up...

McMonster I'll contact with you on elektroda.pl shortly 

[Romain]

Because this is directly linked to PCB tinning, I'm asking here instead of starting a new thread.

I am looking for the good practices on how to do PCB tinning for wave soldering. As rohitdesa and Dave pointed out, if the solder mask opening is too large, the wave will drag the solder along, and the solder thickness won't be not consistent.
On ATX PCBs, the strips are all in the same direction. Should it be parallel or perpendicular to the PCB direction during wave soldering?
What are the good practices?