Diagonal Solder stripes on traces.. Whats the purpose? (Photo included)

[Andy-In_over_my_head]

So my daughters 12v Powerwheel charger was charging at 17.2 volts... the problem was simple to find...
But on the other side of the board, there are diagonal solder lines on 2 of the traces... but they aren't edge to edge..
So couldn't the current blow right past them?   
EDUCATE ME PLEASE!
Thanks in advance!
Photo attached.

[tatus1969]

better conductivity from the additional tin. but it does not really make a big difference, dave once did a video on that.

[CatalinaWOW]

I am guessing that this feature sold a piece of layout software.  Purpose accomplished, regardless of any improvement in conductivity.

[helius]

The intent is obviously to reduce the resistance of those traces, without pooling so much solder that it slumps and makes a short circuit.

[Andy-In_over_my_head]

The intent is obviously to reduce the resistance of those traces, without pooling so much solder that it slumps and makes a short circuit.

Well how is it reducing resistance if its not even the width of the trace?

[Andy-In_over_my_head]

better conductivity from the additional tin. but it does not really make a big difference, dave once did a video on that.

I saw the video where the entire trace was tinned.... but I didn't see one with tinned diagonal.. or strait.. lines.
Not to mention their not all the way from edge to edge...
I think I need to experiment a little to understand this better..

[helius]

The resistance of a long wire is just the resistance of a lot of tiny segments, added together. Reduce the resistance of half of those segments, and the total is necessarily less as well. The reason you don't see this used more often is that it increases heating unevenly (the thin parts heat up more).

[Andy-In_over_my_head]

The resistance of a long wire is just the resistance of a lot of tiny segments, added together. Reduce the resistance of half of those segments, and the total is necessarily less as well. The reason you don't see this used more often is that it increases heating unevenly (the thin parts heat up more).

Forgive me...
I'm trying to make sense of this...
a wire is multiple (or single obviously) strands continuous... so you can get a resistance out of that...
That part I understand...
However if I solder a bunch of wires protruding perpendicularly off of one of those wires, how would that increase resistance if the electrons aren't directed to flow through them?
Similarly (in my uneducated head) wouldn't the electrons just continue flowing past and through them seeing that there are gaps on each side of them? Possibly just making them little solder heat sinks?

[Andy-In_over_my_head]

Also, are there situations I should watch for on my random projects that would require this... or that this would correct?

[tatus1969]

you can imagine the copper trace as a string of single resistors. the tin adds more resistors in parallel with them. calculate the total without and with the extra ones, you'll see that becomes (a little) less.

[tatus1969]

Also, are there situations I should watch for on my random projects that would require this... or that this would correct?

only (barely) makes sense for wave soldered pcbs. better use thicker copper plating for high current designs.

[AG6QR]

However if I solder a bunch of wires protruding perpendicularly off of one of those wires, how would that increase resistance if the electrons aren't directed to flow through them?

It would decrease resistance, not increase it (perhaps you're thinking about increasing conductivity?)

It's often said that electricity takes the path of least resistance, but that's not the whole truth.  Electricity takes ALL the paths available to it, in proportion to their conductivity.  The extra lines of solder provide another path for current to flow in parallel with the PC board trace.  The original trace was a resistor, and the blob of solder is a resistor, so when they're combined in parallel, they form a resistor of slightly lower value.  I would expect the effect to be quite small, though.

[John Coloccia]

My initial guess would have been that they simply removed some solder mask for better cooling.

[AndyC_772]

I think that's unlikely. The solder mask coating is thin, and offers little thermal resistance.

The shiny exposed solder, however, has low surface emissivity, so I'd expect it to radiate heat less effectively than the coated trace.

In any case, the primary path for heat to get out of a copper trace is through conduction into the PCB.

I guess there might be a project for a student or bored engineer to try and measure the effect. Maybe fabricate a test board with two traces on it, pass an equal current through each, then see how warm the PCB gets locally?

[John Coloccia]

But what I'm wondering is this: if adding strips of solder reduces the resistance (which is does), that's still just local to the area around the solder strips. Even though the resistance of the track as a whole has gone down, the uncoated copper is still going to heat up nearly the same as before, right? So then what's the point? Just a slight increase in efficiency so you save $.10 on the electric bill?

Maybe it's just there to transfer heat to that area of the board during wave soldering to reducing warping/stress on the board?

[digsys]

I do a lot of high current P/Supplies, and often leave exposed ~80% of main tracks. Making solder bridges, horizontal or vertical,  DOES reduce losses a little,
and they do it because it quick and dirty. In my cases, IF I need even lower losses, I solder heavy hook up wire along the exposed track. The MAIN reason for
exposed track is air flow cooling. Nearly all our P/Supplies are convection cooling and any exposed metal surface helps a lot !

[T3sl4co1l]

Although the pictured example may not be the best, the technique is almost as good as going from 1oz to 2oz board.  The cost is essentially nil -- the solder is picked up en masse from the wave solder machine.

When you're trying to figure out how in the hell you're going to make a 500W power supply for $40, fractions of a cent matter big time.

Tim

[Andy-In_over_my_head]

I do a lot of high current P/Supplies, and often leave exposed ~80% of main tracks. Making solder bridges, horizontal or vertical,  DOES reduce losses a little,
and they do it because it quick and dirty. In my cases, IF I need even lower losses, I solder heavy hook up wire along the exposed track. The MAIN reason for
exposed track is air flow cooling. Nearly all our P/Supplies are convection cooling and any exposed metal surface helps a lot !

That's a little less confusing..
So for electricity it doesn't have much effect...
however for heat distribution it is helpful and more cost efficient than throwing in heavy hook up wire along that track?

[digsys]

  That's a little less confusing..

bummer, didn't do my job right :-)

So for electricity it doesn't have much effect ...

Yes, but it does give you a nice clean way of adding adding thickness to tracks that need it. I am currently doing a few more P/Supply pcbs that have some 20A tracks that
need 4oz, but also have tiny s/mount comonents. SO I'll do them in 1-2oz and thicken the ones that need it.

however for heat distribution it is helpful and more cost efficient than throwing in heavy hook up wire along that track?

Adding hook-up wire along the track is WAY more effective than plain exposure !! As I said, simply leaving it exposed is not a big help !! Where you have convection cooling,
it does help. This is for our case. As others have said, fabs do it because it is MUCH chaper to run an extra pass through the wave solder than the cost of extra copper.
Solder is not as good conductor as copper, but it's better than nothing.
Hope I've confused you again :-)

[Andy-In_over_my_head]

 [/quote]
Adding hook-up wire along the track is WAY more effective than plain exposure !! As I said, simply leaving it exposed is not a big help !! Where you have convection cooling,
it does help. This is for our case. As others have said, fabs do it because it is MUCH chaper to run an extra pass through the wave solder than the cost of extra copper.
Solder is not as good conductor as copper, but it's better than nothing.
Hope I've confused you again :-)
[/quote]

Actually... you've cleared a lot of fog. I really appreciate it...
I've looked at several power supplies and noticed different styles of this... dashes, stripes, waves... you know....
So it makes a whole lot more sense now..
I'd still like to see a video sometime though... I think it would be interesting...
Thanks again by the way...  Hope to see you on some of my other lame questions I put on here.
I'm thinking of making videos of me trying to figure all of this out...
I don't care for the suscribers or followers or whatever... just think I might feel a little less lame about getting answers..

[tatus1969]

Where you have convection cooling,
it does help.

is it correct to say that multiple smaller stripes further help with convection cooling because it also adds more turbulence to the air stream?

[plazma]

The diagonal solder stripes makes the cross section area bigger --> lower resistance. The diagonals are good because it prevents uneven soldering. One long strip could easily have the solder at one end only.

[digsys]

..... because it also adds more turbulence to the air stream?

Absolutely ! In my electronic load, www.pbase.com/digsys/image/158741424, which I often push to 2KW+ (draining EV battery packs) -
I have 2 high flow fans, front and rear, pushing a shltload of air through the heatsinks. Originally, I could only maintain that power for a few seconds, until I added
"flow disrupters". The extra turbulence, hence "pressure" made a huge difference to getting rid of heat. It basically increased the volumetric amount of air in contact
with a maximum amount of heatsink.

[pbendel]

I think everyone missed the right idea... I think the diagonal stripes of solder protect the trace for a period of time while the solder heats up it will absorb heat from the trace and while the solder changes from solid to liquid phases it will absorb heat from the trace, thus protecting the trace or giving it some surge ability.  Anyone think that is the right reasoning?

[tszaboo]

I do a lot of high current P/Supplies, and often leave exposed ~80% of main tracks. Making solder bridges, horizontal or vertical,  DOES reduce losses a little,
and they do it because it quick and dirty. In my cases, IF I need even lower losses, I solder heavy hook up wire along the exposed track. The MAIN reason for
exposed track is air flow cooling. Nearly all our P/Supplies are convection cooling and any exposed metal surface helps a lot !

It does indeed. Also if it wouldn't help at all, we would still do it. Because common knowledge is that it decreases resistance, so any engineer would still remove the soldermask, so it would seem that we did everything to make the design better.