01005 assembly process—from the board design to reflow
Figure 7. Nozzle at pickup position. Figure 8. Bill board component at the nozzle. Figure 9. Component sensor in action.
• ity reflow soldering in nitrogen improves this and cannot be controlled, it should not
• Feeder unit with fiducial for effect because it generally improves the enter in your process planning.
exact position recognition solder paste’s wetting characteristics.
As with other components, you must general comments
Once the component is picked up, the
create a reflow profile for 01005s that The processing of 01005 components not
vision recognition system must have a
complies with the usual criteria such as only requires very good process knowledge
high resolution and accuracy in order to
gradual warm-up rate/tomb-stoning, and and planning to design the board/product
calculate and correct the position precise
compliance with the maximum permissible for good manufacturability, but it also
enough. It is also very important that
temperature/time limits for components, requires that the production is done under
conditions (Figure 8) that would result
substrates and solder pastes. controlled environmental conditions. It is
in defects later on (e.g. face down or bill
Self-centering does work quite well not necessary to do it in a clean room, but
boarded components) are detected now
for very small components even when it must be done under clean conditions.
and corrected immediately.
lead-free solder is used. Due to the fact Also, temperature and humidity should be
In addition, a placement system must
that 01005 components weigh only 0.04 controlled and kept constant.
be able to verify that no components are
mg, the surface tension of lead-free solder Figure 12 shows a board where a small
lost on the way from the feeder to the
is sufficient to move them. Figure 11 shows fibre had fallen across some pads. This
placement position. Due to the extremely
an example of a test board before and after would create open solder joints or tomb-
small nozzle tip for 01005 components,
reflow. The components were shifted by stones if it was not detected before reflow.
vacuum sensing is not a reliable method
approximately 100 µm and are perfectly
of detecting the component. Therefore, a
aligned after reflow. But this self-centering- conclusions
laser sensor should be used to detect the
effect has limitations. The solderability of As a general statement it can be said that
absence or presence of the 01005 compo-
the pad, the component terminations and the use of 01005 components make the
nent during the pick and place process
the solder paste has to be good, and the product more expensive because of the
(Figure 9).
pad, the printed solder paste depot and higher costs for materials (components,
During touchdown of the component
the termination of the component have to PCB, solder paste, stencil, nitrogen
onto the PCB, the placement force and the
overlap enough in order to avoid tomb- (reflow) and more accurate equipment).
velocity of the Z-axis need to be controlled.
stoning. If all conditions are fulfilled, the The layout and the board design need to
If the speed is too high, the solder paste
self-centering works best and most reliably be done under consideration of all process
gets into contact with the component and
for a shift of up to 50 µm. Since the self- steps to achieve a ‘manufacturable’ product
may splash. Additionally, if the force is too
centering effect is not a process element with sufficient quality. Because of the nar-
much the solder depot will be smashed as
well. The force control is essential to avoid
any mechanical damage to the component
which is usually very sensitive and may
break if forces bigger than approximately
2 N are applied. Finally, during placement
the PCB needs to be well supported so that
no vibrations cause already placed compo-
nents to move out of position.
reflow
Reflow soldering in nitrogen is recom-
mended for 01005 components because
the solder pastes used are usually of the
fine-grained variety (Type 4 and often Type
5), causing them to oxidize more and more
easily than traditional Type 3 solder pastes.
Although one should not depend on the
self-centering effect during soldering,
Figure 10. Standard reflow profile for lead-free
14 – Global SMT & Packaging – September 2008 www.globalsmt.net
Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56