Dave,
The problem of silicones is not the solder joints, but electrical
connections. In the olden days for the telecommunications industry ('60's)
the problem with silicones (so I'm told) is that the silicones would creep
into the space between the crossbar elements, get zapped by the electrical
current (small "lightning bolt") and decompose to silicon dioxide, which is
also an excellent insulator. Because SiO2 is a solid, it also provided a
physical standoff between the crossbar members - badddd news! Today we do
not have physical moving 1 inch pieces of copper, but we do have connectors,
dip switches, etc. Silicones are insidious for their ability to creep
across a circuit pack and get into these areas where there is the need for
variable electrical contact. I can certainly see why any manufacturing
site would not want semi-solid silicones in their building. Now with
respect to silicones that set up hard (like bath tub or weather sealers),
there is actually a leach test that one can do to determine the % amount of
extractable free silicones. Please don't ask me for a reference, as I
haven't done this test in 8 years! I do remember that it involved using a
Freon (gasp!) for the extracting solvent and we used a Soxhlets extractor to
hold the silicones for the several hour test. Hope this helps.
regards,
Bev Christian
Nortel
> ----------
> From: Dave Thomas[SMTP:[log in to unmask]]
> Sent: Friday, July 31, 1998 6:01 AM
> To: [log in to unmask]
> Subject: [TN] Silicone grease around soldered joints!
>
> People
>
> I am looking for some assistance in justifying the non-use of silicone
> grease, ie Dow Corning 304, near soldered joints.
>
> Could someone please supply me with a route to suitable
> documentation/reports to support this?
>
> I understand that if silicone grease should get on a joint prior to
> soldering, there is a very good chance thatthe soldering process will be
> faulty. I am not so clear as to long term effects of silicone grease maybe
> migrating into soldered joints causing degredation and failure in service.
>
> The manufacturing site I am currently working with are unhappy about
> having
> silicone grease in their factory so I am having to find suitable
> alternatives. The difficulty is that my engineers are more than happy with
> silicone, but do not have to worry about long term effects.
>
> Your help would be appreciated.
>
>
> Regards
>
> Dave Thomas
>
> Nothing will ever be attempted, if all possible objections must
> first be overcome.
>
> -- Samuel Johnson, "Rasselas", 1759
>
> ===============================================================
> Dave Thomas Nortel plc
> Principal NPI Engineer, London Road
> European Radio Harlow
> Essex
> Telephone: +44 1279 402901 CM17 9NA
> Facsimile: +44 1279 402100 UK
> ESN: 742-2901
> E-mail: [log in to unmask]
> ===============================================================
>
> ################################################################
> TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
> ################################################################
> To subscribe/unsubscribe, send a message to [log in to unmask] with
> following text in the body:
> To subscribe: SUBSCRIBE TechNet <your full name>
> To unsubscribe: SIGNOFF TechNet
> ################################################################
> Please visit IPC's web site (http://www.ipc.org) "On-Line Services"
> section for additional information.
> For technical support contact Hugo Scaramuzza at [log in to unmask] or
> 847-509-9700 ext.312
> ################################################################
>
################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe: SUBSCRIBE TechNet <your full name>
To unsubscribe: SIGNOFF TechNet
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################
|
