Since many on TechNet have at least some interest in solder mask, should be 
noted that the IPC just published IPC-SM-840, Revision C.

Some significant changes in the "C" rev.: 

- Two performance classes (H, for high rel applications, including military 
and life support systems, and T, for telecom, computers, industrial controls, 
etc.). This is based on the fact that users were not specifying Classes 1 
and 2 as they felt the product was inferior, and thus suppliers began to 
introduce Class 3 masks only. (Bellcore has committed the Calss T 
specification as its own.)

- Upgraded M&IR and Migration test methods

- Defines mask "change" (mask formulation latitude)

- Minimum breakdown voltage

- Mask supplier to provide mask-specific cure test

Also, there is a new test board: IPC-B-25A. For a longer description of 
the new document, see Circuitree Magazine, January 1996, pp. 94-95.

The new revision is available from IPC's order department, 847-509-9700, 
ext. 318. Price is $15 IPC members; $30 nonmembers.

Mike Buetow
IPC Technical Staff
2215 Sanders Road
Northbrook, IL 60062
P: 847-509-9700, ext. 335
F: 847-509-9798
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