What are these dashes for on PCB power traces

[FlapJack]

Does anyone know what these solder dashes are for on the PCB power traces.



This is the back side of a power driver board for an induction cooking burner.

 

[barry]

That's called "thieving". It (supposedly) helps balance thermal distribution across the board. Since you've got large copper areas on the top, when those traces heat up (during soldering, or maybe during operation) they are going to expand at a different rate than the PCB substrate. Presumably, the copper on the bottom will help compensate for that.

 

[ALERTLINKS]

It increases current handling capacity of the track. It is easy to put solder on stripes..

 

[FlapJack]

I was thinking along the same lines of the intention of the dashes increasing the current. But with all of the blank spaces i question weather or not the dashes have any effect. Also with the large difference in resistance between solder and copper it is my understanding that even solid solder along a power trance has minimal effect.

P.S. i think thieving is for balancing the current in large copper areas when the PCB is being plated.

 

[ArticCynda]

It can't be to increase the current handling capacity of the traces because then it wouldn't be dots but continuous lines.
It also can't be to compensate for different expansion coefficients of copper and substrate because copper is tactile enough to handle this expansion (also, shouldn't all boards with a copper pour or plane suffer from the same problem?)

So far I'd have to conclude that this is a purely aesthetic addendum.

 

[ahsan_i_h]

It can't be to increase the current handling capacity of the traces because then it wouldn't be dots but continuous lines.

The solder dashes also increase the surface area of the traces and cause additional cooling during operation.

 

[marce]

A joke I believe, cant see any purpose for them other than to increase the design time, it is one example of design that I would never copy and have never done...
The surface area increase is not that great and it would be hard to calculate how much if any effect it would have on cooling... Thermal conductivity of tin is way below copper, but that is the only possible sensible explanation...

 

[ravindragudi]

If the dashes were meant for balancing the thermal load, then these dashes shouldn't have been tinned, I guess.

 

[marce]

The design is old, one thing that use to happen in't old days was the HASL coating was put on before the solder resist so during reflow you use to get a wrinkled solder mask, this may be to alleviate that (we did all sorts of weird and wonderful things back then.....).

 

[arouse1973]

I personally don't use this, but I always was told by the fab-house it was to help with even plating so other area don't get over plated.
Thanks
Adam

 

[marce]

Nope.... Wrong
Plating thieves are areas of non functional copper added to a design to even out current distribution.

Non-functional metal areas on a surface to be electroplated. Their purpose is to balance the current density during plating to ensure uniform build-up of plated material

As I stated previously early boards often had the HASL done before the solder mask was added, this could cause problems as illustrated by this quote from the IPC CID course notes....

Solder mask may not adhere properly to melting metal surfaces (solder coating, tin/lead plating).
Adhesion is compromised because boards are subjected to temperatures that cause redistribution of
the melting metals. The maximum recommended conductor width, where the coating completely
covers the conductor, shall be 1.3 mm [0.051 in]. If covered conductors of melting metal are larger
than 1.3 mm [0.051 in] wide, there shall be a relief (cross-hatching) through the metal to the base
laminate substrate.
The relief should be at least 2.54 mm square [0.010 square inch] in size and located on a grid no
greater than 6.35 mm [0.250 in]. When conductor areas of melting metal are to be left uncovered,
the design for all class boards shall provide that the solder resist shall not overlap the melting metal
by more than 1.0 mm [0.039 in].

The strong possibility is that this was done for the above reason.....

 

[barry]

Nope.... Wrong
Plating thieves are areas of non functional copper added to a design to even out current distribution.

As I stated previously early boards often had the HASL done before the solder mask was added, this could cause problems as illustrated by this quote from the IPC CID course notes....


The strong possibility is that this was done for the above reason.....

What you are quoting has absolutely nothing to do with the situation at hand. What you quote says that solder-plated conductors need to be cross-hatched to allow proper soldermask adhesion. What we're talking about is thieving on the opposite side of the board.

 

[marce]

Sorry mate you are talking rubbish, where is there any thieving on the board.....
So yes what I am saying has everything to do with the design
the original post...

Does anyone know what these solder dashes are for on the PCB power traces.

Here is another link on thieving I would suggest you have a look at it...
https://www.ee-training.dk/announcement/copper-thieving-confusion.htm

 

[barry]

Sorry mate you are talking rubbish, where is there any thieving on the board.....
So yes what I am saying has everything to do with the design
the original post...


Here is another link on thieving I would suggest you have a look at it...
https://www.ee-training.dk/announcement/copper-thieving-confusion.htm

My friend, go back and read the quote you posted. It speaks of adding relief to copper traces, it says NOTHING about putting little dots on the opposite side of the trace, which is the question here. While true that thieving helps the plating process historically it has been used for thermal balance.

**broken link removed**

 

[marce]

It is not thieving... thieving is adding little dots of copper to the board where there is none... this is adding little holes in the solder resist.
Theiving is for copper balancing during plating... it is copper shapes added to the bare areas of PCBs.... It has always been used for plating balancing

**broken link removed**
**broken link removed**
http://community.cadence.com/cadence_technology_forums/f/27/t/5528
**broken link removed**
http://cr4.globalspec.com/thread/18366/Printed-Circuit-Board-Thieving
http://electronics.stackexchange.com/questions/85633/what-is-copper-thieving-and-why-use-it
Adding thieving patterns to outer layers has very little effect on thermal properties unless the design has been thoughy about and there is a way for the heat to transfer the pattern. The thickness of copper on standard PCBs around 1oz has a limited distance that copper will travel approx. 1-1.5" across a layer, heat dissipation between layers relies on copper patterns being on top of each other and the heat migrating through the pre-preg layers. The best way of thermal management is by the use of copper and thermal vias, with either specialist PCB materials or builds (such as metal core) or using heat spreaders external to the PCB.
IPC-7093 is a good read on this as it deals with the components that tend to have the highest heat density that is going to be transferred through the board and not an external heatsink...

 

[Mattylad]

Stop winding him up guys, we all know that these are an army of solder worms that have eaten their way into the resist and are now busy lining up for more :lol: :lol:

It's not thieving as otherwise it would not be in the copper, it would be separate little dots of exposed copper that increase the amount of copper on the board - these dashes do not do this as the copper is already there so no thieving is being done, all it is doing is partially exposing segments of the copper under the resist.

It has nothing to do with balancing as otherwise it would be copper dots in the areas where there are no traces.

It does nothing for increasing any current carrying capability of the tracks because it is not continual

I wonder if they are simply to indicate that the tracks have a high (lethal) voltage on them - looking at the spacing they may well have.
IMO it's either that or just a waste of good solder - but then we did uses to do daft things like this years ago.

The designer may well just have thought it looked cool so did it. ;-)

 

[marce]

Disagreement's apart regarding thieving... they are either to help heat dissipation (not a lot) or athstetic or maybe as Matt says, show the high voltage traces and allows for easier electrocution when you accidently grab the board.....:lol:

 

[ArticCynda]

show the high voltage traces and allows for easier electrocution when you accidently grab the board.....:lol:

PCBs, assisting natural selection!

Jokes aside, this design is inconsistent: why would one add a slot between (supposedly) high voltage traces to reduce the likelihood of arcing, and simultaneously decrease insulation by breaching solder mask?

 

[Mattylad]

Because one is a plonka!
Simples :-D :-D :-D

I'm sticking to the worms theory

 

[kozacy]

I really agree that it is thieving. And maybe for some reason the designer put soldermask openning for the dots,even though it is not necessary.