Like to endorse and enlarge earlier posts. Apologies for coming in late
on this, (been out a few days).
Vapour phase reflow/condensation soldering was developed originally for
soldering large and massive backplanes/mother boards.
Its principle advantage is to heat uniformly and therefore with minimal
stress to a self limiting max temperature.
So yes the ramp rates can be very rapid (up to 50C/sec.) The process
subsequently transferred to SMT where the lack of delta T was
advantageous compared to the then direct IR ovens.
The rapid ramp was a disadvantage, not because of thermal stress, but
because of tombstoning and the like. The 4C/sec limitation often quoted
for SMT arise from around that period and reflects the uneven heating
and resulting stresses induced by contemporary equipment.
Also in SMT we have to be careful not to explode the high non metal
content of SMT pastes.
In pin soldering using solid solders this is not a concern,
For connector soldering:
[optionally apply and dry liquid - conventionally a resin/rosin - flux
to PCB],
Insert components to PCB
Invert and load washers to pins
VPR.
Fluxcoated washers are normally preferred to flux filled to avoid
concerns as above on flux release.
Most vendors of solder preforms have "standard" sizes for normal
dimension of pins and thickness of boards. A 0.25" thick PCB may present
some issues due to the volume of solder required to fill holes and
limitations on solder preform dimensions, depends on pad size, pin pitch
and so on. I am sure your favourite preform supplier would be pleased to
discuss this with you and simple ways to load the washers. Feel free to
come back to me off line if they don't.
Regards
Mike Fenner
Indium Corporation
T: + 44 1908 580 400
M: + 44 7810 526 317
F: + 44 1908 580 411
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Wednesday, February 25, 2004 8:44 PM
To: [log in to unmask]
Subject: Re: [TN] Soldering .250" thick boards...
Hi Bill!
I'd like to echo Tom's comments about the ability of vapor phase, or
condensation soldering to overcome a lot of thermal mass. I suppose you
would have to use solder pre-forms to accomplish the soldering for
pin-through-hole devices as in your case. My experience with vapor phase
has only been with SMT assemblies though. Tom is right about the price
of the vapor phase fluid too...can run around $600 a gallon!!
A company named Solvaysolexis (formerly known as Aussimont) makes
something they call Galden PFPE (perfluoropolyether) fluids that has
boiling points that range from 150 C. to 260 C.
http://www.solvaysolexis.com/pdf/gald_vapor.pdf
Vapor Phase systems are sold by one of our own Technetters, Graham
Naisbitt of Concoat (http://www.concoat.co.uk/), and there's a company
here in the states called R & D Technical Services
(http://www.rdtechnicalservices.com/) that sell systems.
When you say you use a Airvac solder volcano, are you talking about a
Airvac PCBRM-12? Dynamic solder pot with a bunch of different sized
nozzles? I have one of those here, and I'm having occasional trouble
reworking connectors on some thick back-planes...not as thick as your
.250" boards, but I feel your pain.
I had posted yesterday asking about a Zephyrtronics
(http://www.zeph.com) ZT-6 "Airfountain" to help me with pre-heating and
rework, and I got a response from a colleague of yours who works at
Northrop Grumman Xetron, who has a ZT-6 and several ZT-1's. He said
they're the next best thing to sliced bread when it comes to soldering
or reworking things on a big, thick, heavy copper board. Personally, I'm
going to try and get a demo unit in here as soon as everyone gets back
from APEX.
Hope this helps,
-Steve Gregory-
> Thanks a lot Tom.
>
> -----Original Message-----
> From: Tom Gervascio [mailto:[log in to unmask]]
> Sent: Wednesday, February 25, 2004 8:01 AM
> To: [log in to unmask]
> Subject: Re: [TN]
>
> In a previous life, we used to use a Centech vapor phase reflow to
> reflow large backplanes. May have issues with thermal shock due to the
> large temperature gradient generated when the vapor phase fluid (which
> is very expensive) condenses on the board and gives up the latent heat
> (heats up the board). On the positive side, it is impossible to
> overheat the board and can heat up large thermal masses quickly.
>
>
> Also maybe a preheat of a board before running the boards thru the
> solder wave with some topside flux application (just make sure that
> the flux gets properly activated and cleaned off).
>
> Hope this helps
>
> Tom Gervascio
> Senior Process Engineer
> Sparton Electronics
> (352) 540-4040
>
> >>> [log in to unmask] 02/24/04 02:50PM >>>
> Hi everyone,
>
> I am a Manufacturing Engineering in an area that builds test equipment
> for airborne radar systems. For the past several months Design
> Engineering has
> been giving us a variety of "thick" boards to which to solder thru
> hole
> components. The boards range in thickness up to .250". We have been
> substituting press-in sockets where possible, but they are not always
> available in the sizes we need. So far, in the most difficult
> situations, I
> have been using an Airvac solder volcano. This works fairly well, but
> can't
> be used in all situations, and doesn't always result in flow thru to
> the
> other side.
>
> Is there any other system that would be more appropriate for thick
> boards
> where flow thru is a problem? We are working to J-Std-001B
> Class
> 3. We are ready to go back to the designers (and have gone back to
> them), but I would like to find out if there are other possibilities
> first.
>
> Thanks for any help you can give,
>
> Bill Mengers
> Mfg. Engineer
> Northrop Grumman Corp.
> Baltimore
>
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