It Depends,
1.	4 mil (0.004")  dams are fairly standard and are typically robust, especially on laminate
2.	3 mil dams require extra attention at coat, print, develop, etc.,
	May not hold up on metal and you can't be trying to develop mask out of small vias at the same time.
3.	Conventional LPI technology can't be relied upon for 2 mil dams (the width at the base would be approaching zero due to undercut).  Perhaps some of the 	newer ink jets or LDI machines could do better.
	This dam width should be maintained precisely; it should not vary more than a tenth of a mil regardless of the technology.

I can remember when soldermask was primarily considered an aid for assembly.

Robert E. Welch
Senior Process Engineer
Moog Components Group

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Kelly
Sent: Thursday, July 10, 2014 10:14 AM
To: [log in to unmask]
Subject: Re: [TN] Solder mask tape test

Hi All,
Need some opinions please. The S/M web is .002 to .004 wide. Thanks. Steve Kelly

From: Steven Kelly
Sent: July-09-14 1:56 PM
To: 'TechNet E-Mail Forum'
Subject: Solder mask tape test

Hi All,
Should I have  issues passing the IPC-TM-650 Method https://urldefense.proofpoint.com/v1/url?u=http://2.4.28.1/&k=JoXTMrBQdcVHh4u7l2gEpw%3D%3D%0A&r=wrOQZE2eaR7iVBVXRm5tvw%3D%3D%0A&m=aphp1YI0QY%2BcsFzi3kvQ5Hv4Eickl8kfj9%2BiO9JlYbU%3D%0A&s=a3c815fe97a50d4360e1a1708664aebc561b488cf76ac1a82a7def79da424912 when the S/M web is .002 to .004?
Regards Steve Kelly

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