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Solder resist on large track? (IPC2221)

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toninlg

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solder resist

Hi,

I've read the following in IPC 2221 :
Solder resist coating adhesion to melting metal surfaces
(solder coating, tin/lead plating, etc.) cannot be assured, as
boards are subjected to temperatures that cause redistribution
of the melting metals. When solder resist coating is
required over melting metal surfaces, the maximum recommended
conductor width, where the coating completely
covers the conductor, shall be 1.3 mm.
When conductors of melting metal have a width larger than
1.3 mm, the design of the conductor shall provide a relief
through the metal to the base laminate substrate. The relief
should be at least 6.45 mm2 in size and located on a grid
no greater than 6.35 mm.
Click to expand...
What does it mean? That it is possible that the solder resist couldn't adhere to a track > 1.3mm? If so what does relief
through the metal to the base laminate substrate mean?

Thank you.
 

solder resist adhesion

Depends on PCB construction. Some older style boards had thick solder on the tracks and liquid solder resist applied. When the solder melts the mask could break up on large tracks. Modern PCBs do not suffer from this, the mask is applied before the solder and on plated boards it is not an issue either.
 

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