Charlie,

My *OWN OPINION* is that there is no value for solder float which will be
indicative of
a laminate's ability to withstanding LF assembly in any and all PCBs that
it might be
fabricated into. Any temperature used would only be as a reference value.
A PCB
which is thin, has only single-sided assembly, and has low additional mass
from the
added components, does not need to have a very high solder float
withstanding
capability because the LF assembly temperature will be low, relatively
speaking.

A PCB which is thick, is double-sided reflow, and wave, and hand-soldered,
and
has a high added mass of heat-sucking components, will need to be made
from a
material having a very high thermal withstanding capability.

The increase solder-float temperature isn't "per UL" - UL is responding to
the
suggestion from "the industry" that the SF temperature be 288C.

All of the laminates can pass some form of SF at 288C - the laminate need
only
pass it as a "raw" laminate; what happens after that is that many raw
laminate cores
and raw laminate prepregs get pressed together, sometimes multiple times
if
the board is sequentially laminated, at which point it is a different
animal. Now
some portion of the "final" thermal robustness is dependent on the raw
material,
and some is dependent on the fabrication, and some is dependent on the
assembly processes ...

In my *OPINION*, in this new environment, solder float is no longer a
reliable or
predictive test. It is simply a marker; only one of many; higher is
better, but
how high is needed is a function of many variables, and, how the test is
conducted
makes it more or less valuable anyway.  By conducted I mean: raw laminate
or fabricated multilayer. The Laminators will only sign up for tests on
raw laminates
because that is all they can control - and that would be my position also.

Oh boy ... we are in for some rollicking times.

Valerie





Charlie McMahon <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
12/19/2005 04:58 PM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Charlie McMahon <[log in to unmask]>


To
[log in to unmask]
cc

Subject
Re: [TN] SV: [TN] SV: [TN] Qualification of the Pb-free capable
manufacturers






Hello Valerie:

Would it be fair to encourage the laminate suppliers to place within their
respective specifications sheets whether the material in question can with
stand the increased solder-float as per UL?
In addition, should not the maximum exposure temp (Td) be higher than 288
to
allow for vagaries of individual processing?

What is your view?

Charlie McMahon

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Valerie St.Cyr
Sent: Monday, December 19, 2005 4:51 PM
To: [log in to unmask]
Subject: Re: [TN] SV: [TN] SV: [TN] Qualification of the Pb-free capable
manufacturers

Inge,

This appears to be a presentation from UL showing what services they
provide to the electronics industry. Reading between the lines, it
appears that they are saying that they are increasing their solder
float temperature to 288C as a response to "industry suggested" -
they, UL, did not come up with that number.

There is nothing special about 288C other than it is 550F which is 10%
higher than 500F, which was the solder float temperature to establish
PTH reliability in concert with IPC-6012. I don't know the origin of
the setting of 500F value.

So, 288C is 10% higher than 260C, and if you believe that LF assembly
temps will be up to 260C, then you might want to test to 288C to
determine if you have any margin in the design/material/fabrication
produced PCB.

Werner,

Very few, in fact none so far, of the older or new materials that we have
tested can get to T288 => 45 minutes; we haven't even tried T320. But
unless it is polyimide I have a hard time believing it will make =>25
mins. The only caveat is that the test is not as "standardized" as having
a standard would have you believe!

Regards,

Valerie


---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------