Trust Doug to open a can of worms ;-)
For a quick and dirty look see, I'd recommend some dyne pens like http://www.accudynetest.com/adtpen.html (Google will throw up a million sources including some application and use notes). Basically, the inks have a known surface tension. For uniform and complete wetting, surface tension of the ink must be less than the surface energy of the substrate. Essentially, its an iterative process of trial and error. Eventually, you will find that with 2 successive inks, one will give adequate wetting whilst the other will display immediate dewetting. You therefore know that your surface energy lies between the two values. $0 dynes/cm is our preferred number for wetting and adhesion, and if the values are less than 35 Dynes / cm then you may be in trouble.
Doug, Graham N and others could probably write a big book with potential causes, although as Doug states, it is usually either... The way the solder mask has been processed by the board shop (Taiyo PSR4000 is not the same from board shop to board shop as Graham alluded to) or else it will be something in your process. Could be as stupid as a particular brand of hand cream used by one of your operators, to something as insidious as a situation we came across recently, in which a flux was formulated to contain a fluorosurfactant that was left behind to reduce surface energy to eliminate solder bridging. Worked real well for eliminating bridging, but coating over the top was a nightmare!
If you do run into a surface energy issue, then you will spend a lot of time auditing your board shops and your own processes. Your coating manufacturer should be able to help you get to the bottom of the issue, but we're always here to help if you need.
Best Regards,
Phil.
Phil Kinner
Business Director
Chase Electronic Coatings
PLEASE NOTE NEW ADDRESS & PHONE #
Chase Electronic Coatings
295 University Av, Westwood, MA 02090 USA
Cell:+1 781.789.4986
DDI:+1 781.332.0741
www.humiseal.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
Sent: Thursday, May 06, 2010 8:15 AM
To: [log in to unmask]
Subject: Re: [TN] Wrinkling of conformal coating
Doug,
I wish the substance was old... and smart, like us!
You are putting me in a tough situation here. How to check surface energy, what should be the good values and how to fix it if not OK?
Thanks,
Ioan Tempea, ing.
Ingénieur Principal de Fabrication / Senior Manufacturing Engineer T | 450.967.7100 ext.244 E | [log in to unmask] W | www.digico.cc
N'imprimer que si nécessaire - Print only if you must
-----Message d'origine-----
De : Douglas Pauls [mailto:[log in to unmask]]
Envoyé : May-06-10 8:10 AM
À : [log in to unmask]
Objet : Re: [TN] Wrinkling of conformal coating
For what it is worth, I think that the coating is simply too old. Isn't the cause for most wrinkles? Some days I just slay me.
One thing that you might check as well is the surface energy of your masked surface. Some of the other suggestions from the forum are your more likely culprits, but you may be seeing some form of dewetting as well, that causes the coating to pull away from one area and congregate in another. Sometimes it is not the mask, but how the mask has been processed that is the issue.
Doug Pauls
Graham Collins <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 05/05/2010 02:13 PM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to [log in to unmask]
To
[log in to unmask]
cc
Subject
Re: [TN] Wrinkling of conformal coating
For my guess I'll go with either too thick, or contamination on the panel
making it try to dewet.
Questions: is this a new problem on a product you have been successfully
coating until now? Have you measured the thickness to ensure it is within
normal range?
Suggestion: Could you do two thinner coats and let it flash off a bit
between coats?
regards,
Graham Collins
Halifax Production Engineering
L-3 communications Electronic Systems
(902) 873-2000 ext. 6215
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
Sent: Wednesday, May 05, 2010 3:59 PM
To: [log in to unmask]
Subject: [TN] Wrinkling of conformal coating
Dear Technos,
Back to orange peeling, this time concerning conformal coating, please see
http://ipc-technet.groupsite.com/galleries/photo/124230
The coating is applied with an Asymtek Century machine and is a Conap 1170
acrylic.
· The board is left curing in ambient temperature, no
acceleration. Starting with an even coating, in about 20-30 minutes the
liquid seems to move towards a certain area (no rippling at this moment).
After another 10-15 minutes the rippling effect sets in.
· We thought that due to the almost 2 minutes lag between the
coating of the first and last image, the drying of the coating layer is
not even and the one side curing first pulls on the liquid at the other
end. So we've cut the panel in 2, accelerated the machine, the problem is
still there.
· The boards are laid as flat as possible, maybe not perfectly
horizontal, but not worse than others with the same coating, that do not
show any issue
· Just to make it more difficult: grabbed a non-populated panel
from the stores, coated it, placed on the same flat surface, and guess
what: no issues.
The PCB has Taiyo PSR 4000 MP soldermask.
So I would need your guidance in clarifying where is this coming from and
how to fix it.
Thank you,
Ioan Tempea, ing.
Ingénieur Principal de Fabrication / Senior Manufacturing Engineer
T | 450.967.7100 ext.244
E | [log in to unmask] <mailto:[log in to unmask]>
W | www.digico.cc <http://www.digico.cc/>
N'imprimer que si nécessaire - Print only if you must
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