One cannot make a PCB that is better, in any aspect, than the material on
which it is made.

One can always, however, make an inferior PCB from good materials.






"Stadem, Richard" <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
11/03/2005 11:04 AM
Please respond to TechNet E-Mail Forum; Please respond to "Stadem,
Richard"


        To:     [log in to unmask]
        cc:
        Subject:        Re: [TN] board material for high temp


A question for the fabricators:
Are there other fabrication aspects besides the material properties that
determine whether a board can withstand lead-free temperatures? For
example, if the pwb material properties conform as described by Dr.
Whittaker below, but the lamination of an umpteen-layer board stackup
was not done correctly, even though the material does not break down or
approach Td, the board itself can still delaminate, measle, warp, or
have other problems?

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Edwin Louis
Sent: Thursday, November 03, 2005 9:45 AM
To: [log in to unmask]
Subject: Re: [TN] board material for high temp

Board vendors are more interested in temperature to decomposition which
is defined as the temperature at which a laminate loses 5% of its mass
in a TGA cure. Generally, if the Td is greater than 340 deg.C it is
considered Lead-free compatible.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Whittaker, Dewey
(AZ75)
Sent: Thursday, November 03, 2005 9:56 AM
To: [log in to unmask]
Subject: Re: [TN] board material for high temp

James and others,
You have had some good responses, but as Richard said when he quoted Sir
Doug,"It depends", is still the best answer. It depends on the layer
count, smallest PTH, smallest via, aspect ratio, thermal management of
your design, number of reflow processes prior to ship, max reflow
temperature[ eutectic vs. RoHS compliant( Lead-Free)], time above
liquidness, need to support rework, life cycle (1-3 years; 5-7 years;
20+ years) and end use environment.
As it stands right now, going up the scale in a slash sheet sort of way,
you have the following:
* IPC-4101/21, /24, /26, /121, /124, /101, /99, and my personnel
favorite /126.
The attributes that are key are as follows:
* Tg - I favor minimum 170 C, others agree a minimum 150 C is adequate.
* Moisture - 0.5% or less
* Thermal Resistance
  T260 - 30 minutes minimum
  T288 - 5 minutes minimum( some believe 2 minutes is sufficient)
  T300 - AABUS( as agreed between user and supplier)
* Decomposition Temperature - I would like 350 C ( 5% wt. loss) general
consensus 330 C
  minimum
* Z Axis CTE - I want 3% or less, general consensus 3.5% maximum
* CAF Resistance - AABUS
* Curing Agent - Although this is a dicy subject, I'll mention it
anyway. Phenolic cure systems presently outperform traditional FR4
formulations as it pertains to maintaining functionality while being
exposed to a greater number of higher thermal excursions.

The Rev B of IPC-4101 will include additional rhetoric, as well as the
new slash sheets, to help you make an informed choice as it pertains to
laminate selection, but it can not do it alone. IPC-6012, IPC-2221,
IPC-600 and the Via Protection Task Group will also have to be revised
for them to be an effective reference source to deal with all the new
performance requirements of today's Market Place. I will, with others be
working to make that happen.
Chairman of IPC-4101
Wannebee Poet Laureate of Tech-net
Dewey

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of James TerVeen
Sent: Wednesday, November 02, 2005 12:14 PM
To: [log in to unmask]
Subject: [TN] board material for high temp

What does everyone us for board material for High temperature solder
applications.   We have a new product that will require the use of high
temperature solder.   Will the use of conventional FR4 be sufficient.

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