What will ablate is a function of the power density in the laser spot. So a
frequency tripled Nd:YAG or Nd:VO4 laser will not necessarily ablate
anything unless the power, spot size, focal point, among other variable are
properly set. The good thing about the UV lasers is the fact that the
solder mask can be photochemically decomposed, not photothermally ("burned")
removed. The optical characteristics (reflectivity, etc.) and ablation
threshold of soldermask should be quite different than gold, so it should
not be a given that a "laser" will remove the gold. The higher ablation
threshold of Cu is typically factored into the process for laser drilling
blind vias, since the UV laser parameters are adjusted to not blow through
the Cu. Unfortunately the ablation threshold of the resin in the
glass-resin structure in the PCB is very similar to that of the solder mask
so you do need to take care not to blow the resin off the outer dielectric
layer around the copper pad. In my former job with Siemens we did a lot of
work with frequency doubled Nd:VO4 lasers (535nm, emerald green) and even
worked with material suppliers to add absorbers to the dielectric to
facilitate ablation to enhance blind via drilling, especially in RCC
materials. The UV is absorbed by most materials making control to not
damage underlying materials a bit more sophisticated. CO2 lasers are also
widely used by PCB makers for via drilling. These lase in the IR range
where they ablate material photothermally so this frequency is not the first
choice for solder mask ablation.
Best regards,
Leo
Leo M. Higgins III, Ph.D.
Vice President, Technical Operations
ASAT, Inc.
3755 Capital of Texas Highway, Suite 100
Austin, Texas 78704
office phone 512-383-4593
mobile 512-423-2002
[log in to unmask]
www.asat.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of John Burke
Sent: Tuesday, May 09, 2006 12:26 PM
To: [log in to unmask]
Subject: Re: [TN] Laser Ablation of Soldermask
Very interesting!!! Did you use a frequency tripled YAG?
John
-----Original Message-----
From: Anslow, Phillip [mailto:[log in to unmask]]
Sent: Tuesday, May 09, 2006 9:09 AM
To: 'TechNet E-Mail Forum'; 'John Burke'
Subject: RE: [TN] Laser Ablation of Soldermask
Ahha,
Could I just add:
If on ENIG boards, be careful as laser will ablate gold off and leave
exposed nickel - beware non-wetting problems and also possible ablation of
PCB surface. Just experience being shared on attempted salvage.
Phil.
-----Original Message-----
From: John Burke [mailto:[log in to unmask]]
Sent: 08 May 2006 17:59
To: [log in to unmask]
Subject: Re: [TN] Laser Ablation of Soldermask
*** WARNING ***
This mail has originated outside your organization,
either from an external partner or the Global Internet.
Keep this in mind if you answer this message.
Ah,
I believe you are trying to remove mask from the pads?
If you are doing this on enig boards be advised that you will also have to
"finish" them with Entec as you will expose bare copper if that is the case.
John
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kevin Glidden
Sent: Monday, May 08, 2006 7:09 AM
To: [log in to unmask]
Subject: [TN] Laser Ablation of Soldermask
Hi all,
We have lasers available to us in house, used for other processes, but I am
wanting to use these lasers for laser ablation of solder mask on our PCBs.
I am new to the laser process and operation, but have experienced
technicians to rely upon. Any general or specific advice in terms of
intensities, speed, or other factors?
Thanks,
Kevin
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