Ioan,
In general, I have used this rule of thumb:
<30 dynes/cm - you will see problems with adhesion and wetting.
30-35 dynes/cm - you will still see problems with adhesion and wetting, but not as much as under 30.
35-40 dynes/cm - generally decent adhesion and wetting but occasional issues
40+ dynes/cm - good adhesion and wetting.  Collins specifies >44 dynes/cm for its solder mask.

Douglas Pauls | Sr. Technical Fellow | Electronics AMT
COLLINS AEROSPACE
400 Collins Road NE, MS 108-101, Cedar Rapids, IA  52498  USA
Tel: +1 319 295 2109 | Mobile: +1 319 431 3773

-----Original Message-----
From: TechNet <[log in to unmask]> On Behalf Of Ioan Tempea
Sent: Monday, March 11, 2024 2:42 PM
To: [log in to unmask]
Subject: [External] [TN] Surface energy for conformal coating

Hello Technos,

Some many years ago I have discovered, with help from this illustrious panel, the existence of the dyne pens. Have used them for a while and them moved to microelectronics, where I have spent 11 years without any contact with conformal coating. So I've kinda forgot some details.
Where I work we have the Surface Analyst device, measuring contact angles and this is supposed to obsolete the use of dyne pens.

The trouble is I can't remember what dyne values are related to good coating wetting. Or even better, which contact angles are preferred?

Can anyone help?
I'm interested in both solder masked PCBs and Au plated ceramics and the optimal values I believe differ from PCB to ceramics.

Also, do you have any good articles or textbooks to recommend on this matter?

Thanks,

Ioan