I have also seen the problem with incompatible solder masks. From what I
have seen the flux 'Balls' together like water on an oily surface. This
results is some areas of the PCB being staved of flux. It all depends on
what type and make of flux is being used and the quantity that is applied.

Getting back to the dross problem. Could it be that you wave machine is due
for pot maintenance. If there is a lot of dross inside you wave channels
this can be released in small particles by the flow of the solder through
it.

It could also be a problem with your solder pumps. They could be dragging
dross from the top of the solder and pumping it through the wave.

Either way, these small 'lumps' of dross will not be displaced by the flux
that has been applied. They will still want to stick to any bare
copper/HASL/gold,nickel that they encounter.

Just my observations.

Mark Austin
===== Original Message from [log in to unmask] (TechNet E-Mail Forum.) at
6/09/00 13:21
>A question...you said "...solder mask may be unsuitable...this is quite a
>common
>problem..."
>
>I've not heard of this before, of course I'm a fabricator, not an
>assembler, but I'm
>confident if our customer's were having this problem (i.e. "...this is
>quite a common
>problem") I'm sure they'd be screaming... Would you please expand on those
>comments,
>thanks.
>
>Franklin D Asbell
>
>Brian Ellis wrote:
>
>> OK, Darren. It is not easy to be categorical but I suggest you are
>> losing in at least one of two directions, maybe both.
>>
>> 1) So-called "no-clean" fluxes usually have relatively small amounts of
>> activators which tend to sublime/evaporate at temperatures exceeding ca.
>> 50°C. It sounds like you may simply not have enough left on the board
>> when it hits the wave. Try wicking down the preheat a little at a time
>> until the results improve, if this is the case. Perhaps a little more
>> flux sprayed on would help, as well.
>>
>> 2) It may also be that your solder mask is unsuitable or incompatible
>> with the flux or has been insufficiently cured. This is quite a common
>> problem, especially with some of the glossy masks and dry-film types.
>>
>> This list is not exhaustive, but you have a 95+++% chance that the
>> answer lies above.
>>
>> Brian
>>
>> Darren Goh wrote:
>>
>> >
>> >
>> > Hi,
>> > I would really appreciate some help here..
>> > I am running some mixed board (thru holes with SMD) over wave.. after
>> > the wave, I discovered almost 80% of the boards are spatter with small
>> > lumps of solder dross on the under side... (between three to five
>> > counts of them)
>> >
>> > I am using Tamura no-clean flux and on board preheat temp is peak at
>> > 100degree for 10 sec. the whole preheat zone runs at 80 sec..
>> >
>> > am using Alpha Metal solder bar ..and adopting spray fluxer
>> > technology, no clean process..
>> >
>> > I hope that someone could highlight and share with me the reason (if
>> > possible solution) for the formulation of solder dross on the under
>> > side of mixed technology boards after wave.
>> >
>> > thank you very much
>> > Darren
>> >
>> > DID:- (65) 2493448
>>
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