I do not know of any standard that provides a guideline for reflectivity
of the soldermask - the more light the mask absorbs the more matte and
more reflective the more gloss.  

Issues are noted on both ends - the gloss materials can inhibit image
acquisition on fiducials/features covered with mask and can also have
issues with conformal coating.  Gloss materials have less propensity for
contaminate entrapment and generally have better cleanliness levels
after soldering but can have issues with conformal coating adhesion.
Years ago there was issues with gloss mask and solderballing, but I have
also seen issues with this condition on matte finishes and it may be a
function of the brand/process rather than finish.  

Matte materials generally look "dirty" as non-reflective surfaces do not
hide surface conditions.  Matte surfaces have more surface
area/topography and tend to be more difficult to clean post soldering.
A no-clean flux looks much better on a gloss material than matte
material.  

We use a "middle of the road" material that is termed "semi-matte", but
has a light absorption of ~ 50% and this seems to service all needs
fairly well.  Mask manufacturers have latitude on what they call a
material so brand X may be semi-matte and brand Y may be semi-gloss and
they both look identical.  I would stray from specifying with matte or
gloss and qualify materials that work well for your assembly.  I
recommend developing a mask matrix in your PCB spec that allows a
variety of materials to be used by fabricators.       
   

Jeffrey Bush
Director, Quality Assurance and Technical Support

VERMONT CIRCUITS INCORPORATED
  76 Technology Drive - POB 1890
    Brattleboro, Vermont 05302
      Voice: 802.257.4571.21 Fax: 802.257.0011
           http://www.vtcircuits.com
 

-----Original Message-----
From: Matthew Park [mailto:[log in to unmask]] 
Sent: Tuesday, May 10, 2005 2:27 PM
To: [log in to unmask]
Subject: [TN] PCB soldermask spec

Hi all,

Which IPC document spells out soldermask surface finishes like glossy,
semi-matte or matte? IPC-SM-840 does not mention any spec's about
soldermask surface finishes. How do PCB vendors create matte surface
finish? Is there any industry standard I can use when specifying a
soldermask surface finish like matte?

I am used to seeing glossy soldermask finish. What are
process/manufacturing issues for using matte soldermask finish ?

Thanks
Matthew P.

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