Article on Printed Circuit Fabrication (September 1999 issue)

Written by Karl H. Deitz and Edward F. Hagan

The Process of Dry Film Lamination

Figure 3:  Nip pressure profile with straight rolls	Figure 4:  Nip pressure profile with crowned rolls

[Extraction of articles]

When pressure is transmitted to straight lamination rolls, they tend to bend and form an uneven roll footprint on the resist (Figure 3).  The footprint is narrow at the center of the rolls and wider at the ends.  This means that the pressure on the resist at the center is less than at the ends.  The result is poorer resist conformation at the center and a tendency for the dry film to wrinkle (which will be discussed shortly).  

Laminator suppliers are aware of this phenomenon and try to build the rolls as sturdy as is practical.  Residual roll bending can be compensate for with rolls that are "crowned" (Figure 4).  A crowned roll has a rubber covering that is thicker in the center than at the edges and changes gradually from center to edge, resulting in a curved profile.

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