Hello Patrick,

Patrick Ducas wrote:
>
> Hi, I would greatly appreciate any help or any recommendation in the
> following subject...
>
> We are having solder residues on gold fingers of PCBs, those are seeing
> immediately after the reflow oven (it's a recirculation convection reflow
> solder system). A visual inspection  has been done after the printer
> machine at high magnification and nothing showed up. We were thinking that
> the problem was from the printer machine since a long time but we found
> that it is not the case today.
>
> I suspect that the problem is coming from the reflow oven but I dont see
> the problem mechanism. The reflow atmosphere is nitrogen and the ramp up
> temperature at the entrence of the oven is relatively high, arround 3.4
> C/sec.
>
> Does anyone of you have an idea concerning this problem, thanks in advance.

Allow me to share our own experience, a similar problem to yours:

We were reflowing PCBs with gold-plated traces on both the top and
bottom sides. SMT components populated only one side, but surprisingly,
we were seeing solder splashes on the gold plated traces at the bottom
side which were not populated with any components at all. We eventually
traced the problem to be due to the aluminum PCB holders that we were
mounting the PCBs on to carry it from screen print to reflow. The
holders are needed to standardize the rail widths on our machines to
reduce conversion time. It was discovered that solder balls from the
solder paste accumulated on the holders as they are reused on the
system. And these eventually reflowed and found its way onto the
gold-plated traces on the bottomside of the PCB which was in direct
contact with the holders. Our solution was to punch out the holders
ensuring that the PCBs sit on them with the gold traces at the bottom
not in contact with any metal.

--
Luke B. Mendoza
Electronic Assemblies, Inc.
http://www.globe.com.ph/~eai

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