Charlene,
The weak link when using photoimagable soldermask is the mechanical
alignment of the artwork (films) and the skill of the soldermask technician.

Both LPI and dryfilm soldermasks are imaged after they are applied to the
PCB, therefor it is the imaging (film alignment) which is critical, not the
application of the soldermask material or it's type.

Larger fabrication panels and films make alignment more difficult
because they suffer from greater expansion and contraction than smaller
panels. It is in the fab houses best interest to use large panels because
they reduce the cost of PCB manufacturing (larger panels=more PCB's
per panel=less labor and less wasted materials).

It may be helpful to talk to the cam operators at your fab house.  Explain
your soldermask clearance requirements, they may be unaware of the panel
size issues (turnover is very high at most fab houses and technicians are
often inexperienced).  They are probably willing to work with you to achieve
the best possible registration.  If they won't or can't then shop around, there
are fab houses that can work with 2 mil clearances (1 mil ??).

Good Luck,

Mark Koitmaa
TechServ
www.TechServInc.com


----------
From: 	Charlene Dwyer[SMTP:[log in to unmask]]
Sent: 	Thursday, September 05, 1996 10:23 AM
To: 	[log in to unmask]
Subject: 	Soldermask-misregistration

     Does anyone know if there is a particular soldermask that will keep 
     tighter registration.  For instance, is a liquid soldermask able to 
     keep a tighter registration than a dry film?  Currently, we allow for 
     a 4mil misregistration in our soldermask opening.  We would like to 
     bring that number down to 2 or 1mil on a very tight board we have 
     (that has cooper covering the ground pads-causing the ground pads to 
     have a larger shape) without having the manufacturer scrap alot of 
     boards.  Our plating is immersion nickel/gold.
     
     Thank-you
     
     Charlene Dwyer
     [log in to unmask]

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