I waited for some actual practitioners to respond to this before adding my two penneth,
which is:

For Au/Sn and other comparable melting point alloys such as the high lead silvers and high
lead tin silvers you will need to peak at around 310-320C.
For fluxless soldering you will need a forming gas reducing atmosphere.
The process times on fluxless soldering are quite long so you may need several minutes
above alloy melting point depending on the size and geometry of your work.
You will also need time to ramp up to these temperatures.

These requirements probably eliminate 98% of SMT oven suppliers and I suspect those that
can meet them will turn out to be oven suppliers who are also in the SMT market rather
than SMT specialists.

You can shorten the times and use nitrogen by using flux. Type R has plenty of activity at
these temperatures. The nitrogen is necessary to prevent flux char and to make residues
easier to remove. If you need more information in this area come back.

Mike Fenner
BSP

----- Original Message -----
From: Ingemar Hernefjord (EMW) <[log in to unmask]>
To: <[log in to unmask]>
Sent: 20 September 1999 07:37
Subject: Re: [TN] Fluxless soldering (AuSn) with SMT reflow ovens


> Morning, Jeff,
>
> We changed to vacuum oven, because of too much built-in voids when conveyor soldered.
That was large semiconductor chips for heatspreaders (the metal plating outgassed). X-ray
showed significant improvement. To get max wetting, we also plasma clean heatspreaders
before assembly starts. Guess you ask for semi chips also. Don't know what help this may
give you...
> Ingemar Hernefjord
> Ericsson Microwave Systems
>
> -----Original Message-----
> From: JEFF PERKINS [mailto:[log in to unmask]]
> Sent: den 17 september 1999 18:36
> To: [log in to unmask]
> Subject: [TN] Fluxless soldering (AuSn) with SMT reflow ovens
>
>
>
>
>         Is anyone doing fluxless soldering with AuSn eutectic preforms in SMT reflow
ovens (inline conveyor, not batch)?
>
>                 Any problem achieving temperature (eutectic point 280C)?
>                 Any problems in Nitrogen environment?
>                 How about preforms of other compositions?
>
>
>         Thanks,
>                 Jeff Perkins
>                 Epitaxx
>
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