By the way have we not met? at Alenia/Rome. I visited Dr Selleri to study
his laser welder.
Inge
On 22 February 2012 20:15, Inge Hernefjord <[log in to unmask]> wrote:
>
> Hi Luigi,
> I agree about ghosts. I have thought so too many a times. In this case,
> the ghost can be bustered by having a look in Wassink, I quote:
>
> The cause of solder balls can be
> (i) Incorrec distribution of flux, resulting from maladjusment of fluxer
> or transporting jigs, or from board material that id badly wetted by flux.
> (ii)oxidation of solder at the position where the board loses contact with
> the solder bath or of wave (also a fluxing faultl).
> (iii)contamination of the solder.
> (iiii) incorrect pre-drying of the solder paste
> (v) use of poor quality of the solder paste.
>
> Another way to find the ghost is to investigate the process window. Tt
> consists of so many parameters, that I prefer to send the troubleshooting
> map to you offline instead.
>
> Then we can continue the discussion.
>
> Before I close, I can tell you that we have seen similar issues and I
> recall that we saw such swarms of microballs only in the VP line. When the
> subject is passing the firsr zone too fast, volatiles are still within the
> paste. When in the lower part, the instant heat makes the slurry boil and
> before the solder has liquidified, a number of solder particles escaped and
> were spread around, more or less. The size variation mirrors the paste's
> nature namely solder particles from nn um to xx um.
>
> The map will come in minutes, got to find it first..
>
> Inge
>
> -
>
>
>
> On 22 February 2012 07:33, <[log in to unmask]> wrote:
>
>> Hello everybody.
>>
>> Any idea about random presence of microballs (diameter 0.1 to 0.5 mm)
>> beneath some chips (R and C 0805, 1206,1210, 1812) ?
>> We use a SnPb process with a vapor phase oven.
>> We use same types of PCB, same process on same SMT line in a clean room
>> from years and the balls are randomly present from some months now.
>> They could be present in one lot of PCB and not the following; beneath a
>> component on one PCB and not on the same component on other PCB; we have
>> balls one day and not the day after; the balls disappear for weeks and
>> re-appear after; ...
>> I have checked different lots of solder paste, origin of PCB's, all
>> parameters of printing, P&P and the cleaning (co-solvent station). The
>> thermal profiles are same.
>> As it's hi-rel production I cannot change easely products and process.
>> I suspect a process parameter but which ?
>> I ask myself if there is not a ghost in the line .. :-)
>>
>> Best regards.
>>
>> CANTAGALLO Luigi
>> Technology Engineer
>>
>>
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>
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