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Subject:
From:
Lee Whiteman <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Lee Whiteman <[log in to unmask]>
Date:
Tue, 19 Jul 2005 11:19:26 -0400
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Larry,

You're correct in that the cooling profile for the reflow soldering and
wave soldering will be similar. 

Most consideration is given to reaching the peak temperatures. However,
the cool down portion of the thermal profile should be controlled.

Cool Too Fast could thermal shock solder joint and component. However a
fast cool down will result in the solder joint having a smaller grain
size. This should improve the solder joint’s fatigue resistance. I've
heard of stories where folks would "quench" with cold air the hardware
right after soldering but I never personally seen it in the shops I
supported or tried it. I would adjust the cooling fans at the end of the
reflow soldering equipment I had. With the wave soldering equipment, the
ones I had did not have this feature so we let it air cool as you are
doing. 

Funny thing was that I a prior life, we had an area air ionizer directly
on the output of the wave solder. When it was turned on by the operator,
it did change the thermal profile. We had to move it because it would
thermally shock - not ESD shock -  the components. These components were
ESD Class 0 devices so we had ionizers all over the place to protect
them.

Cool Too Slow will result in a solder joint with grainy appearance due
to the larger the grain size within the solder. There is the potential
for excessive intermetallic layer growth which creates brittle solder
joints.

Typically, the cool down rate is 3 to 4C / sec until ~  130C. This
depends on the alloy used.

With respect to the fluxes, my biggest concern would be if the fluxes
were baked on during the soldering process. Baked on fluxes and flux
resides will be difficult to clean.

Sorry for the confusion.

Hope this helps.

Good Luck.

Lee Whiteman
Senior Manufacturing Engineer  
American Competitiveness Institute
E-Mail: [log in to unmask]
Ph: (610) 362-1200 x208
Fax: (610) 362-1290

This message is for informational purposes only and does not supersede,
modify, or create any agreements with ACI. Information contained in this
message does not bind ACI or its affiliates to any commitment, either
express or implied, unless ratified in writing by an authorized
representative. 


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Davis, Larry
Sent: Tuesday, July 19, 2005 8:37 AM
To: [log in to unmask]
Subject: Re: [TN] Lead free oven


Lee,
Could you please clarify "cooling side of the profile"?  I have always
thought of the reflow process in the same way as the wave process.
During wave soldering, once a board exits the soldering area it begins a
rapid descent back to room temp.  Why would reflow soldering need to be
any different after the relow zone?  Is it related to flux residues?

Thanks, 
Larry Davis

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Lee Whiteman
Sent: Monday, July 18, 2005 3:26 PM
To: [log in to unmask]
Subject: Re: [TN] Lead free oven

David,

I fooled around with reflow soldering ovens with between 3 and 5 zones.
The good news is that they were able to reflow solder Lead Free
hardware, reaching the peak temperature of about 240C.

The bad news is that the profiles were very steep. In my opinion, in a
production environment, the already smaller window for processing Lead
Free solders will be reduced because the profiles will be too steep,
thus exhausting the fluxes (which are manufacturer dependent). In one
case, I mimicked the solder paste manufacturer's recommended profile
correctly, but the peak temperature was reached in zone 4 of a 5 zone
oven - messing up the cooling side of the profile.

The deltas across the board were similar to SnPb, but I was not
comfortable with the results. In addition, depending upon the quality
(solderability, thermal mass) of the materials (boards, components,
solder paste) you will be running, your oven may not be as flexible or
as forgiving as you may want.

In a prototype shop, where I was building very low volumes, I would run
with it. In production, I want better control to account for boards and
components that are less than optimum. Therefore I would consider
getting an oven with a minimum of 7 zones.

For example, in one shop I went to, they had a 10 zone oven. They
generated the thermal profile and built Lead Free soldered hardware with
SAC-305 with no problems. I have a 7 zone oven in my shop and we run
SnPb and Lead Free hardware of varying thermal masses and geometries
fine. For additional details, give me a call off-line.

Hope this helps.

Good Luck.

Lee Whiteman
Senior Manufacturing Engineer
American Competitiveness Institute
E-Mail: [log in to unmask]
Ph: (610) 362-1200 x208
Fax: (610) 362-1290

This message is for informational purposes only and does not supersede,
modify, or create any agreements with ACI. Information contained in this
message does not bind ACI or its affiliates to any commitment, either
express or implied, unless ratified in writing by an authorized
representative. 


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David Tremmel
Sent: Monday, July 18, 2005 5:00 PM
To: [log in to unmask]
Subject: [TN] Lead free oven


Hello all,

We have a reflow oven with 4 zones and is capable of a maximum
temperature setting of 500°C.  We will probably be reflowing lead-free
assemblies in the future and I would like some feedback as to whether or
not our oven could be used for such a purpose.

My concern is not having enough zones to provide the controlled
temperature deltas needed but also allowing proper flux activation.

As always, I appreciate whatever feedback I receive.


David Tremel

_________________________________________________________________
Consigue aquí las mejores y mas recientes ofertas de trabajo EE.UU.
http://latino.msn.com/empleos

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