In a previous life I looked after process engineering in a shop that
made soldered/brazed waveguide components using either propane or oxy
acetylene torches so I reckon I'm something of an expert...
Anyway, the point is that the soldering/brazing mediums don't see the
temperature of the flame as you heat the parts to be joined and then
apply the brazing rod or solder keeping the flame away from the joint.
The purpose of the flame is to heat the parent parts to temperature -
capiliary attractration draws the braze/solder into the joint. How do
you know you've reached temperature? You apply the correct flux to the
joint and the flux changes colour when it reaches the correct
solder/brazing temperature. Then you apply your solder/braze rod.
If you're going to do it in production you'll need skilled operators.
It's not the most difficult job in the world once you know what to do
but anyone starting from scratch you will struggle to produce joints
that are hemetically sealed but not covered in 'gorilla snot' (excess
solder) as Peter has just observed.
Even in our production envoronment we still had a fair amount of rework
to repair joints that were not 100% air tight.
Regards,
[log in to unmask] wrote:
>
> 1000 degrees is about the temperature of the hottest part of an
> oxy-acetalene welding torch, the likes of which I have often used to repair
> cars and other bits of machinery by melting bits of steel together. Please
> note - "melting" and "steel".
>
> Are the parts being heated, or the solder joints, actually seeing this
> temperature, or are they such a large heat sink that much of the heat is
> dissipated? i.e. where are you measuring the temperature?
>
> At 1000 degrees, I would have thought the brass would have melted and the
> st st parts be somewhat warped. The silver soldering would have come apart
> as well, and as others have said the solder would be a nasty drossy lump of
> oxide. Methinks there has to be more to this story than meets the eye -
> what is this engineer's background? What has he designed before - and did
> it work?
>
> Sounds to me like it's not a very controlled, or controllable process, this
> welding torch to do a bit of soldering. I confess I once (before many
> people were born) tried to solder repair panels onto a car using a welding
> torch. My theory at the time was that if I could apply enough heat
> generally at soldering temperature, the buckling of the car's bodywork
> would be minimised. I did manage to get the panels to solder after a lot of
> trial and error, but the overall effect was not as predicted - the panels
> still warped, the solder did tend to be very drossy unless I used a
> carburising flame (oxygen-poor) and kept the flame from getting too close
> to the panels themselves. Net conclusion - an unsatisfactory waste of a lot
> of time - and flux and solder, and body filler to cover the warps in the
> panels.
>
> Peter
>
> "Diamond, Pat" <[log in to unmask]> 25/07/2002 04:05 PM
> Sent by: TechNet <[log in to unmask]>
>
> Please respond to "TechNet E-Mail Forum."; Please respond to "Diamond, Pat"
>
> To: [log in to unmask]
> cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
> Subject: Re: [TN] Overheated solder alloy
>
> Dave,Roger,
>
> this is not being used on a PCB or wiring harness, I will try to explain
> but
> it's a bit tricky.
>
> One of our "Engineers" has come up with an RTD (Resistance Temperature
> Device) assembly design which comprises of silver brazed peice parts
> (st/steel),which are then joined to a tube (brass) internally, using solder
> rings made out of solid 60/40 (both 20 & 18SWG) and using a flame torch to
> heat the parts up (this was measured at 1000+ deg.C).
>
> Added to this he has designed in HMP (221 deg. C) solder as a "sealant"
> around the top of the assembly to seal the rod and the tube, also soldered
> using a flame.
>
> Oh I forgot, he has specified Multicore "Arax" as the fluxing agent.
>
> Will these joints be reliable after seeing that temperature?
>
> I would have thought the silver braze would also re-flow at the
> temperatures
> used, would they be affected?.
>
> Is this guy crazy or is he a genius?
>
> Does any of this make any sense!
>
> regards,
>
> Pat
>
> -----Original Message-----
> From: Dave Hillman [mailto:[log in to unmask]]
> Sent: Wednesday, July 24, 2002 5:34 PM
> To: [log in to unmask]
> Subject: Re: [TN] Overheated solder alloy
>
> Hi Pat! You will have molten Sn60 solder at a temperature of 1000C! Tin
> boils at 2603C and Lead boils at 1750C so you won't start vaporizing the
> Sn60 solder alloy until you get near the 1750 C point. I just have to ask -
> why the concern of 1000C? Your printed wiring assembly will be quite toasty
> and you would have molten solder running on the floor before you reach the
> 1000C mark!
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
> "Diamond, Pat" <[log in to unmask]>@ipc.org> on 07/24/2002 08:38:17 AM
>
> Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
> to "Diamond, Pat" <[log in to unmask]>
>
> Sent by: TechNet <[log in to unmask]>
>
> To: [log in to unmask]
> cc:
>
> Subject: [TN] Overheated solder alloy
>
> Technetters,
>
> this may seem like a crazy question but.....what would happen to 60/40
> solder alloy at temperatures of 1000 degrees C?
>
> regards,
>
> Pat Diamond
> Weston Aerospace
>
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--
Eric Christison
Mechanical Engineer
STMicroelectronics
33 Pinkhill
Edinburgh
EH12 7BF
tel: +44 (0)131 336 6165
fax: +44 (0)131 336 6001
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