REVISTA ROMÂNĂ DE AUTOMATICĂ - IPA SA

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REVISTA ROMÂNĂ DE AUTOMATICĂ
a. b.
The apertures with tombstoning were type 2
for 0.125 stencil (figure 6a-0603 case, OSP
finished) and for 0.150 stencil, type 1 (figure
6b-0402 case, OSP finished, 6d-0402 case,
NiAu finished), also type 2 for NiAu , 0603
case and 3, 4, for chemical Tin.
Fig. 7. VPS thermal profile
c. d.
Fig. 6a-d. Solder joints follow up apertures type
For NiAu pads finished, cases type 0402,
0.150mm stencil, the number of tombstoning
was bigger, but at the limits, with a small
angle lifting. It is important that NiAu for
0.125 stencil, chemical silver and HASL for
both stencils have not tombstoning. The
solder joints resulting after stencils apertures
type 2 and 3 present to much solder. In
connection to the tombstoning results, the
conclusion is that 2 and 3 apertures type
especially on 0.150mm stencil, NiAu pads
finished and case smaller than 0805, must be
avoided. The parameters of VPS process are
position on levels, period on position and
heating power. The SLC504 machine offers
20 levels with 0 – 100% power range. In
order to obtain the optimum thermal profile,
the authors used temperature sensors to
measure temperatures distributions on pcb
surface. The result emphasizes differences
between temperatures measured on PCB
surface and machine reference temperature.
Tab. 3. Tombstoning for 0.125 Stencil Printing
Tab. 4. Tombstoning for 0.150 Stencil Printing