Mel,
surface tension of lf-alloys is higher. Therefore you will find more bridgings
and solder balls.
gebhard
"Mel Parrish" <[log in to unmask]> on 16.07.2003 15:48:04
To: "'TechNet E-Mail Forum.'"
<[log in to unmask]>, Gebhard
Neifer/MEGAMOS@MEGAMOS
cc:
GLT:
Class.: None
Subject: RE: [TN] High temp pastes for wave soldering...
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I'm trying to recall some work we did in the early 90s with Lead Free alloys
because it seems to me that there was a reduction in surface tension rather
than an increase. In fact, we had serious issues with accelerated solder
climb on leads like SOTs that starved the connection area because the
available solder was up the lead rather than in the connection.
Solderability and flux performance being a given.
Is that incorrect - or - is it alloy specific?
Dr John would know but he has moved on to bigger fish and it appears that
Dave H. is on vacation.
Mel Parrish
Director, Training Materials and Resources
Soldering Technology International
102 Tribble Drive
Madison, AL 35758
256 705 5530
256 705 5538 Fax
[log in to unmask]
www.solderingtech.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of
Gebhard.Neifer
Sent: Wednesday, July 16, 2003 5:12 AM
To: [log in to unmask]
Subject: Re: [TN] High temp pastes for wave soldering...
As far as I know, surface tension of lead free alloys is higher (-> poorer
wetting, more thermal energy to achive same wetting).
Flux is an issue for sure. Flux has to be designed for higher temperatures,
otherwise it will cause voids during reflow.
Gebhard
Guy Ramsey <[log in to unmask]> on 15.07.2003 17:35:16
Please respond to "TechNet E-Mail Forum." <[log in to unmask]>;
Please respond to Guy Ramsey <[log in to unmask]>
To: [log in to unmask]
cc: (bcc: Gebhard Neifer/MEGAMOS)
GLT:
Class.: None
Subject: Re: [TN] High temp pastes for wave soldering...
Flux is definitely an issue, even when soldering to the lead-free lead
finishes. Though I must say, we don't have the answer here. We saw
icicles as well, even hand soldering. I think the surface tension is
lower in these alloys and it compounds the problem. Clearly the fluxes
that were designed to activate and disappear at temperatures around 220
are going to be gone by 240. Dave Hillman are you out there?
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dave
Chapman
Sent: Tuesday, July 15, 2003 10:39 AM
To: [log in to unmask]
Subject: Re: [TN] High temp pastes for wave soldering...
Is there an exemption from Lead Free requirements for solder paste? And
is that also the case for wave soldering PCBs?
Dave Chapman
-----Original Message-----
From: Guy Ramsey [mailto:[log in to unmask]]
Sent: Friday, September 06, 2002 3:14 PM
To: [log in to unmask]
Subject: Re: [TN] High temp pastes for wave soldering...
Getting the paste isn't too hard. But, reflow (25-40 degrees above
liquidous) temperature for those alloys is hazardous for FR-4, and many
components. Ceramic chip caps and thick film resistors might be okay but
this is clearly over the top for most plastic IC packages. We have done
some experimenting with direct attach and forming-gas to ceramic using
these alloys. One day we ran an FR-4 board though the oven without
thinking. What came out of the oven would best be described as ash with
body.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Friday, September 06, 2002 3:20 PM
To: [log in to unmask]
Subject: Re: [TN] High temp pastes for wave soldering...
Hi Steve,
Hope you don't mind, I put a subject in the subject box for your post...
As far as through-put issues with your dispenser, why not print your
epoxy. You would do the whole board in well less than 30-seconds, and
have much better accuracy and consistency than you could ever expect
from a dispenser.
As far as high temperature pastes go, you would need one of the
high-lead alloys in order to be above the typical solder pot temperature
of 500° F (260° C). Getting these alloys in paste form is going to be
challenge as well, you can bet that it's going to be a custom order with
a minimum buy too.
A few of those alloys are:
° F ° C
Sn10Pb90 514 - 576 268 - 302
Sn10Pb88Ag02 514 - 570 268 - 299
Sn05Pb92.5 Ag2.5 536 280
My two-cents...
-Steve Gregory-
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