REVISTA ROMÂNĂ DE AUTOMATICĂ - IPA SA

REVISTA ROMÂNĂ DE AUTOMATICĂ
37
5. Conclusions
The quality analysis and tombstoning
appearances situations demonstrated that the
type 2 and 3 apertures assure solder paste on
pads in excess. As upshot the wetting angle
of solder joints are close to 90°, the limit of
quality acceptance. Also, the solder paste in
excess offers condition for spread solder balls
on pcb surface. The theoretical analysis and
practical results show the importance of
solder paste deposit’s axial dimension
compared to chip component axial dimension
as a tombstoning factor.
Based on the practical results of experiments,
the generally accepted criteria for a chip,
component solder adequacy, the joint should
extend up the component termination for a
minimum of one-third of the component
height, or 0.4 mm, whichever is less, the
tolerance of chip components cases, the
variability of pad dimensions, the authors are
proposing the following requirements for
stencil design regarding chip components
assembling in vapour phase technology:
radial apertures dimension, Xa :
Xa = W+H (4)
axial apertures dimension, Ya :
Cp – Ya = S, Cp + Ya = L=T, Ya = (L+T) /
2 (5)
stencil thickness: 0.125mm
As a result, the team defined the necessary
criteria in order to obtain optimum thermal
profile by measuring temperatures directly on
pcb surface: preheating with 1.4 °C/s until
185-190°C and go to range of melting point
with 0.66 °C/s until maximum temperature
230 °C.
References
[1] T. C. Cucu, N.D.Codreanu, I. Plotog,
"Reflow process using lead free materialsbasics
and comparison with tin-lead process",
Proceedings of the 2005 Interntional
Symposium for Design Technology and
Electronics Packaging (SIITME 2005), Cluj-
Napoca, Romania, September 22-25, 2005,
pp. 250 - 255.
[2] I. Plotog, S. Jianu, C. Turcu, T. C. Cucu,
N.D.Codreanu, “Multi-criterial Approach for
Implementing of Lead-free Technology”, 4th
European Microelectronics and Packaging
Symposium, May 21-24, Terme Catez,
Slovenia, pp. 301-306.
[3] I Plotog, S. Jianu, C. Turcu, A. Stan,
T.C.Cucu, N.D.Codreanu, DFM Concept for
Wave Soldering Technology, SIITME 2006,
Iasi, September 2006 Romania
[4] Klein Wassink, Soldering in Electronics
(2nd Edition), Electrochemical Publications,
Port Erin, Isle of Man, Great Britain, 1989
[5] S. Jianu, I. Plotog, C.Turcu, A. Stan,
T.C.Cucu, N.D.Codreanu, Reliability Aspects
for optimal Implementation of Lead-free
Technology, SIITME 2006, Iasi, September
2006 Romania
[6] ***, Internet web sites related to
DFM topics.
[7] ***, www.ipc.org
AR4-7.doc