Hello All,
Has anyone ever run any tests with different flux type (ROL, REL, etc.),
different Pb-free solder bar(SAC, SN100C etc.)?
Looking back and forth, all the tests were accomplished with the use of
SAC solder bar. What's going on if with SN100C solder bar? Thanks.
Best Regards
Charming Chan
PCBA Engineer
John Goulet <[log in to unmask]>
发件人： TechNet <[log in to unmask]>
2008-11-04 10:45
请答复 给 TechNet E-Mail Forum; 请答复 给 jgoulet4
收件人： [log in to unmask]
抄送：
主题： Re: [TN] AW: [TN] How to improve solder filling and
wetting contact angles for thermal vias at wave soldering process.
We designed a test PCB with various hole sizes and several rows had a DIP
pattern where each hole had a wagon wheel ground pad connecting to the
inner layers. The wave process used the same temperature profile 225-230F
for Pb-free boards and the same conveyor speed. We also tested the
difference in contact time and wave dynamics between the Electrovert wave
with the chip wave of the original design, about 4 inches back from the
contour wave. In the electrovert the chip heats the board, burns up much
of the flux for the 1 to 1.5 seconds, then cools. Some of the 5-6 seconds
in the contour wave is lost in remelting the solder then wets with
whatever flux is left depending on the flux used. We also ran the boards
over the Vitronic Delta-max with the smartwave for a continuous contact
time which allows the flux and solder to work together. The angle of the
smart wave pushes the solder up the holes very well. The main wave
continues the process and could solder the same boards at !
a faste
r conveyor speed. Electrovert now makes a new setup where the chip wave is
closer to the contour wave. In both cases we used nitrogen inserted wave
to increase wetting and have a shiny solder joint.These non-functional
engineering boards were about .085" thick.
The result was similar to your findings that a standard hole size with
.005" clearance between the lead and the PTH wall or greater worked well.
You can compensate for standard designs by slowing the conveyor to add
more contact time. Larger hole to lead clearances helps to overcome the
sluggish wetting of Pb-free solder and increase the conveyor speeds. The
leads with the wagon wheel design tied to ground were the big indicators
of what works and what doesn't relative to flux and wetting
angles/pressure and continuous wetting of some systems.
We had similar results with the required contact time, temperature and
flux on the robotic selective solder tests.
I hope these extra points and observations are helpful.
-------------- Original message --------------
From: Pete Houwen <[log in to unmask]>
> Michael,
>
> The testing we did was undertaken to see what we might need to change in
> our existing designs, after we had made a decision on laminates and
finish that
> would be suitable for our particular needs. So the only finishes we
tested
> were ImAg and ENiG, using no-clean, and .062 boards. We assembled boards
> using our existing lead/hole/pad ratios, and then ratios on either side
of
> those. What we found was that there was not a large difference, but the
> ratios in that chart worked well, and fortunately (with no intended
bias) were
> our existing design standards. The hole sizes are slightly larger than
what had
> been normally used in the industry for SnPb solder, it turned out that
while
> they weren't optimal for our old SnPb wave, they are for SAC. We did
note
> that in all ratios, the ImAg seemed to fill a bit better, though both
finishes
> passed the 75% requirement.
>
> This hasn't been a cure all, we have found assemblies failing the 75%
> requirement on occasion, but only when our manufacturinjg process was
not
> properly controlled. So there isn't a lot of room for error, but that's
> lead-free.
>
> Pete
>
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