Using solder-coated tracks/planes to increase current handl

[Steve Harvey]

Hi,
I am working on a re-design where the current product is based on a
8-layer 1oz PCB and is being re-configured to a 6-layer PCB to save
cost. In some areas of the design, it is desirable to minimise the
resistance of certain current-carrying tracks which are currently
paralleled on all 8 layers. The change down to six layers will inrease
the effective resistance in these critical areas and I am consdering
the use of "solder coating" on the "solder-side" to effectively
increase the conductivity in this area (which is wave soldered) to
compensate.

I have no direct design experience of doing this but have seen
examples in other products (power supplies and automotive ECU modules)
and would appreciate any advice as to the benefits and pitfalls. I am
sure that this process has a well know "name" but not knowing what
this term is, I would find the WWW of little help or guidance.

I am working on the assumption that all I need to do is to edit the
solder resist away in the areas that I need filled and the soldering
process does the rest but I am sure there are some dos and don'ts that
I need to know first.

Of course the resistivity of tin/lead is significantly higher than
copper, so the coating will need to be signicivantly thicker than the
copper traces to compensate for the missing internal layers.

Thanks in advance


Steve Harvey
steveharvey [at] dsl [dot] pipex [dot] com

 

[Nick Naylor]

steveharvey@lineone.net (Steve Harvey) wrote in message news:<9da33165.0404280506.4df7cc48@posting.google.com>...

Hi,
I am working on a re-design where the current product is based on a
8-layer 1oz PCB and is being re-configured to a 6-layer PCB to save
cost. In some areas of the design, it is desirable to minimise the
resistance of certain current-carrying tracks which are currently
paralleled on all 8 layers. The change down to six layers will inrease
the effective resistance in these critical areas and I am consdering
the use of "solder coating" on the "solder-side" to effectively
increase the conductivity in this area (which is wave soldered) to
compensate.

I have no direct design experience of doing this but have seen
examples in other products (power supplies and automotive ECU modules)
and would appreciate any advice as to the benefits and pitfalls. I am
sure that this process has a well know "name" but not knowing what
this term is, I would find the WWW of little help or guidance.

I am working on the assumption that all I need to do is to edit the
solder resist away in the areas that I need filled and the soldering
process does the rest but I am sure there are some dos and don'ts that
I need to know first.

Of course the resistivity of tin/lead is significantly higher than
copper, so the coating will need to be signicivantly thicker than the
copper traces to compensate for the missing internal layers.

Thanks in advance


Steve Harvey
steveharvey [at] dsl [dot] pipex [dot] com

Have you considered using more copper on the 2 outer layers? I know
most board houses offer 1.5 Oz and 2 Oz. This may increase the cost
of the 6-layer board, but should still be less expensive than the
8-layer board.

 

[N. Thornton]

steveharvey@lineone.net (Steve Harvey) wrote in message news:<9da33165.0404280506.4df7cc48@posting.google.com>...

the effective resistance in these critical areas and I am consdering
the use of "solder coating" on the "solder-side" to effectively
increase the conductivity in this area (which is wave soldered) to
compensate.

I have no direct design experience of doing this but have seen

Its automatically a great deal thicker, no problem there.
The usual thing is to keep the width of unmasked track narrow so that
excessive solder build up does not happen - big lakes of solder can
run while still molten, or can build up enough strength to put real
mechanical strain on the copper.

In use some cracks may occur in the solder, but they are no problem.
If you draw the R network that the cu/solder makes you'll notice a
crack has little effect. Ditto thermally.

For maximum conductivity while keeping solder dimensions within
bounds, a dotted mask pattern can be used.

Finally the thicker less flexible solder does not have anything like
the vibration resistance that the copper has.

And really finally, inserted wire links are one other option.


Regards, NT