Title Intrusive reflow with SNIC paste
Bob Willis
The following covers examples of good and defect coating processes and some of the problems
experienced in industry.
Intrusive reflow with
SNIC paste
production we normally use a 0.006" 150 be inserted first. It has often been difficult
µm or 0.005"stencil if the board has been for engineers to automate the odd-form
correctly designed. assembly process for connectors due to
The paste volume printed on the the need to invest in additional odd-form
surface of the board is determined by the equipment. Now with selected placement
pitch of the connectors and the standoff machines having the capability to insert all
features of the connector body. The the popular surface mount shapes and odd
selection of the stencil thickness is also form parts, it opens up the opportunity for
determined by other fine pitch parts on greater use of PIHR technology. However,
the board. Good design of the connectors as is often the case when a single connector
allows the paste volume to be maximised is used, it is normally inserted manually.
Figure 1. Close-up of stencil.
on the surface of the pads and onto the The Harting 96 way edge connector is
surface of the solder mask. often used in our hands on training
The close-up of the stencil in Figure 1 sessions as it is one of the largest and
Normally connectors in pin-in-hole intru-
shows it positioned over the surface of a more challenging connectors to reflow
sive reflow have the greatest impact on re-
board prior to printing. The connector pin due to its mass. It has been used many
flow delta T because they are BIG, so what
to hole size increase is 0.010" with a 0.080" times on production lines and provides an
happens with a higher reflow temperature
foil aperture. The finished hole size is what ideal demonstrator for our through-hole
with tin/copper solder paste?
should be stated in the manufacturing reliability work at NPL.
Let’s get straight to trials as most
data package. The reason for this is that Reflow soldering was conducted with
engineers know the benefit of reflowing
the range of different surface finishes can two processes, convection in air on a BTU
through-hole parts!
impact the ease of insertion. During these reflow oven and vapour phase with an
The pin in hole intrusive reflow
trials, copper OSP, tin, silver, gold and ASSCON 6000 system. Both processes are
(PIHR) process starts with stencil printing
HASL finishes were used. commonly used for lead-free manufacture
the surface of the board with solder paste.
After printing, SMT components in Europe.
Traditionally stencil printing is conducted
would normally be placed on the surface The reflow profile of the connector
for surface mount terminations, but
of the paste prior to insertion of the achieved a maximum temperature of
with PIHR solder paste it is also involves
connectors into the pasted through holes. 245˚C when processed in the BTU
printed over the through hole pads, resist
Depending on design, the connectors may Pyramax 100 convection reflow oven.
and into the plated through holes. In
Figure 2. Reflow soldering profile. Figure 3. Vapour phase soldering profile.
52 – Global SMT & Packaging – October 2009
www.globalsmt.net
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