The wording of the IPC-SM-840D is a little vague. 3.8.1 is a requirement for the material, not the application of it. It is a requirement of the soldermask manufacturer.
Table 3.1 shows that this requirement does not fall on the fabricator. If there is a minimum thickness or breakdown voltage, you need to put it on the drawing (AABUS)
It appears like they are controlling the materials, but not really controlling the minimum application.
Carl
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of kwood716
Sent: Tuesday, September 23, 2008 9:12 AM
To: [log in to unmask]
Subject: Re: [TN] Solder mask thickness
Phil,
I'm not sure why this is becoming an issue lately other than cost. I have been told by more than one reliable source that 1mil thick is not a problem but some vendors try to save resources and make it thinner. I've called out SM thickness of 1mil minimum for many years with no problems. Lately, some overseas vendors claim they can only do 0.4mil thickness. I received a PCB with what they claim is the standard (0.4mil) and I could almost see through it and promptly rejected it. Bottom line is that mask needs to be 1mil minimum and if it is any thinner then it is up
to the vendor to prove that it can handle 500VDC of insulation. Hope this helps. Ken
_____________________________________
Kenneth J. Wood
President
Saturn PCB Design, Inc. [log in to unmask]
2737 Bishop Lane (407) 340-2668
Deltona, Fl 32725 fax: (386) 789-2765 www.saturnpcb.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Nutting
Sent: Tuesday, September 23, 2008 8:29 AM
To: [log in to unmask]
Subject: [TN] Solder mask thickness
Good afternoon,
OK, here is this afternoon's question. Solder mask thickness, what is the "industry standard"? We currently specify 0.001" thickness and this may be fine on a large area when tested via IP TM-650, 2.5.6.1. Now use 2 ounce copper traces in a normal board configuration. Our board vendors are stating that they cannot hold the 0.001" thickness at the edges of the etch, it is more like 0.0003". And if we spec 4 ounce or 6 ounce I'm sure it doesn't get any better.
How are you specifying solder mask thickness on your heavy copper weight circuit boards?
Do your board vendors use two coats of mask to obtain the thickness needed to comply?
IPC-SM-840 section 3.4 says it must meet the requirements of section 3.8.1, thickness of 0.001" at 500 Vdc.
Your guidance is requested.
Thanks,
Phil Nutting
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