Solder paste print
and printed using all the same printing obtained from a PCB supplier and sections Bob Willis is a process engineer working in
parameters. The surface fiducial marks of the film applied to the surface and left the electronics industry, providing training,
can easily be seen through the film. After for as long as they would be in production. consultancy and product failure analysis. Bob
printing, the quality of paste definition After removal from the surface of the also offers on site workshops on conventional
can be determined. Alignment, paste copper, the test copper sheet is held under and lead-free for customers. He will be running
volume and any paste squeegee out from a running water tap. Any contamination workshops at ITRI Merlin Circuits during
the apertures due to excess pressure, print on the surface of the copper will cause October-November and at IPC MidWest and
speed and damage to the stencil can easily the water to de-wet, demonstrating SMTA International in September—details at
be assessed. contamination has been left by the film
www.bobwillis.co.uk. Bob is happy to assist you
Today we use a range of PCB surface adhesive. There may be some minor de set up and optimise production lines for users
finishes. Some are more affected by wetting but not gross contamination. and also provides conferences and workshops
cleaning and the type of cleaning material worldwide.
used than others. In order of performance,
after any cleaning process, copper OSP is
worst and solder-coated is best, along with
gold over nickel. Silver and tin are in the
middle. One of the nice things with solder
coating is that any surface contamination
is ruptured as the solder reflows.
Figure 3. Lead-Free Solder Paste & Printing guides.
The paste print procedure guide above
and examples of printing criteria are
available online at
SolderingStandards.com
It’s important to check that the film
does not affect print quality of surface pad
solderability. Trials should be undertaken
on materials. The water break test is a
simple test to see if any residues are left
on the surface. A clean copper sheet is
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