I can see your thinking, but an earlier poster was correct: although the
melting point of the solder is higher than the wave soldering temperature,
if the higher melting alloy sees the wave it will dissolve in it in much the
same way as say electroless gold (MP 1064C) on a PCB does.
If you still want to go ahead, be aware that there are a number of higher
melting point alloys you could use in the range 270 - 280C. These are
generally characterised as having a high lead content with smaller additions
of tin, silver, indium and so on to 100% according to the precise melting
point you are looking for. This high lead content means the joints will be
slow to form and dull in appearance. At the higher range you will be near to
caramelising the flux and if you need to remove it you may find (according
to the supplier) some difficulty in doing so effectively as it will tend to
bake on.
Because of the small usage of these alloys in wire form - compared to Sn63 -
you may not find they are all available flux cored and you will need to
apply flux separately. Here I would recommend you use a paste flux which you
can apply from a syringe. (ours is called Tacflux, other suppliers will have
their own names). This is less messy and more controlled than painting on
liquid flux and also gives you the opportunity to get more easily cleanable
or no clean types suited to the higher melting alloys.
You will need to use a decent iron capable of operating at the higher
temperatures and delivering the heat correctly without damaging the board
and pad adhesion, and pay attention to proper tip dressing and control so as
not to get tip dewetting.
Alternatives might be to use a dispense solder paste and hot air repair
tool.
Good luck
Kind Regards
Mike Fenner
Applications Engineer, European Operations
Indium Corporation
T: + 44 1908 580 400
M: + 44 7810 526 317
F: + 44 1908 580 411
E: [log in to unmask]
W: www.indium.com
Leadfree: www.Pb-Free.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of makshuwing
Sent: Tuesday, February 19, 2002 11:18 AM
To: [log in to unmask]
Subject: Re: [TN] High temperature solder wire
Hello eter,
Adhesive dispensing, chip placement, reflow(glue curing), manual insertion,
then wave soldering are our normal processes. After reflow we sometimes find
some mis-aligned chips or missing components. The area of glue in contact
with the surface of the mis-aligned chip could be less than normal and the
adhesion force is insufficient to protect the chip from dropping off during
wave soldering. Therefore we want to use high temp solder to solder the
mis-aligned chips prior to wave soldering. We know that we could detach the
parts after reflow and hand solder the parts after the wave soldering but we
think adding hi-temp solder is the simpliest way since there is no
detachment process is involved.
Eric
----- Original Message -----
From: "Peter Barton" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, February 19, 2002 12:41 AM
Subject: Re: [TN] High temperature solder wire
> If you are going to the trouble to hand solder these parts on why not fit
> them after the wave solder process and just tack them on, applying a dab
of
> rework flux first, then reflowing the solder that will be present on the
> pads? Saves the difficulty of using high temp solder pre-wave, and quite
> likely excessive solder on the joints post wave (the solder in your bath
> will wet to the high temp. joints already made). I have seen a similar
> problem when tack soldering large multi way connectors with high temp.
> solder pre-wave.
>
> Regards,
>
> Peter Barton
>
> ===== Original Message from [log in to unmask] (TechNet E-Mail Forum.) at
> 18/02/02 13:40
> >Hi all,
> >
> >We are currently using adhesive to glue chips on PCB and then run the
board on reflow oven
> followed by wave soldering. After the reflow process we need to rework
some
> chips occasionally due to chip miss-alignment or missing. To do the rework
> we have to remove the original glue, re-glue the chips and let the board
go
> through the reflow process again. Now we want to eliminate this loop by
> using hi-temp solder wire (melting point 268-302 degree C) to solder the
> reworked chips without adhesive, then let the reworked board directly go
to
> wave soldering with solder pot temperature around 245 degree C.
> >
> >Has anyone using this method seen problems?
> >
> >Eric
>
>
> -----------------------------------------------------------------------
> Peter Barton
>
> ACW Technology Ltd
> Dinas Isaf West
> Tonypandy
> Mid Glamorgan. CF40 1XX Wales
>
> Tel: 01443 425200 Fax: 01443 436882
>
> International Tel : +44 1443 425200 Fax : +44 1443 436882
>
> E-mail: [log in to unmask] Website/URL: www.acw.co.uk
>
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