SMT crystal flux removal

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Hi all,

We use a ceramic package SMT crystal (connected to a PIC) on a PCB and
it's hard to get flux out during assembly. Units that weren't cleaned
properly pass testing only to come back a few months later when the
flux becomes conductive enough to stop the oscillator.

For those of you who have run into this problem, what was your fix?

--
Brad Eckert

Re: SMT crystal flux removal


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If you have flux underneath the chip after assembly, you need to find another
assembly house.


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Re: SMT crystal flux removal
On 2 Oct 2003 14:26:33 -0700, the renowned snipped-for-privacy@tinyboot.com (Brad

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I suggest changing the flux. Talk to the technical people at the flux
manufacturer. Maybe go back to the older types.

Best regards,
Spehro Pefhany
--
"it's the network..."                          "The Journey is the reward"
snipped-for-privacy@interlog.com             Info for manufacturers: http://www.trexon.com
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Re: SMT crystal flux removal
Brad - a suggestion based on some study but little testing:

If you are using a rosin based flux with "accelerators", a two part
cleaning solvent is reportedly needed; one polar and the other non polar.
The non polar component is for the rosin and the polor for the
"accelerators".

If this description matches the flux used, you might try adding some
alcohol (polar solvent) to your cleaning. Isopropyl is most conservative
of those generally available, ethanol (barring government required addins)
next and methanol most active.

Testing with some components soldered to scrap boards could be helpful.
If you try this or anyother possible cures, do post the results.

Hul

: Hi all,
:
: We use a ceramic package SMT crystal (connected to a PIC) on a PCB and
: it's hard to get flux out during assembly. Units that weren't cleaned
: properly pass testing only to come back a few months later when the
: flux becomes conductive enough to stop the oscillator.
:
: For those of you who have run into this problem, what was your fix?
: Brad Eckert

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