However, only a few would be able
to tell you that it all depends on the copper weight. In order to make the
design process simple and ward away complications during the manufacturing
phase, here is a brief demonstration of how and why the width of the line
depends on copper’s mass.
Furthermore, you will find some
almost-universal rules for trace width vs. copper weight, alongside other vital
contemplations when using heavy copper.
Copper Weight and Trace Width
Throughout the etching process,
copper traces are merely secluded from the top by a dry film or a tin plate.
This means that as the copper is etched, the trace sides are also etched. It
wouldn’t be wrong to say that the process of etching is isotropic.
As a result, the thick copper necessitates
broader trace and space, and the traces are finished in a trapezoidal shape. Stated
below are some guidelines for trace width vs. copper weight:
|
Preparatory Copper
|
Minimum Trace
|
Minimum Space
|
|
0.5oz
|
0.003″
|
0.003″
|
|
1oz
|
0.005″
|
0.005″
|
|
2oz
|
0.008″
|
0.008″
|
|
3oz
|
0.012″
|
0.012″
|
|
4oz
|
0.016″
|
0.016″
|
What would be the case if you
need a tighter trace and space? In general, you can replicate the layer that needs
heavy copper, and then divide the copper weight in halves. So, for instance, if
you require 16 mil lines and 8 ounce copper, reproducing the layer and using 4oz
copper would be the ideal choice.
Basically, there are 2 added contemplations
to heavy copper typically on the external layers. Foremost and fundamental is the
soldermask.
When making use of liquid
soldermask, several coats are needed to sufficiently guard the heavy copper
traces. However, this issue is alleviated using 3D printed soldermask.
Nonetheless, this technology is rarely being used and it is available in
limited colors.
Secondly, the surface mount pads often
get jeopardized with heavy copper. While the Gerber file spells out the trace
width from the bottom of the trace, the SMT takes place on the top. With heavy
copper, chances are bright that the top of the SMT pad may turn out to be a
number of mils thinner than planned, causing difficulties in placement and
producing a debilitated solder joint.
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