Hi Ted,
We went the rounds on this as well and came up with a note that is working for us.  We have boards that go up to 16 layers and get heated about 6 times during fab and assembly.

MATERIAL: 
USE ISOLA 370HR OR SONOSITE APPROVED EQUIVALENT MATERIAL PER IPC 4101A
/24/26/29/98/126; NON DICEY CURED.
	COPPER CLAD HIGH TEMPERATURE FR4 CLASS EPOXY GLASS RATED UL94V-0:
	MINIMUM STARTING COPPER THICKNESS: 0.25oz. EXTERNAL; 0.5oz. INTERNAL.
		(SEE PLATING FOR FINISHED COPPER THICKNESS.)
	MUST BE RoHS COMPLIANT AND SURVIVE LEAD-FREE ASSEMBLY.
	MAXIMUM REFLOW OF 260 DEG. C (6 PASSES)
	Td RATING: >340 DEG. C
	Z AXIS CTE: <3.5% (50ºC to 260ºC)
	Tg 170 DEG. C OR HIGHER
	TTD T260/288 (TMA) >60 MINUTES

Cherie Litson, CID+
PCB Design Tech Lead
SonoSite, Inc.
 
IPC Certified Instructor
Office: 425-951-1306
Cell:    206-619-8844
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Klefisch, Ted J
Sent: Monday, August 27, 2007 11:19 AM
To: [log in to unmask]
Subject: [DC] base materials for lead-free PCB's

Hello Designers,

I work for a medical OEM.  We will soon be producing RoHS-compliant
PCBA's.  I am not sure what exactly to include in the fab notes to
specify the PCB base materials for compatibility with lead-free assembly
temperatures.

For pre-RoHS boards I have included a note on the fab drawing that
specifies "FR4, copper-clad laminates" plus board thickness and UL
rating requirements.  Our boards are generally .062" thick and 8-layers
or less.  As far as I know, we've always used conventional FR4.

What would you suggest I include in a fab drawing note to assure that
the boards survive the higher assembly temperatures?  Is it enough to
specify decomposition temperature alone or should glass transition
temperature also be called out?  Td=330C?  Tg=150C?

I really appreciate your suggestions and advice.

Thank you.

Ted Klefisch, CID
Covidien
444 McDonnell Blvd.
Hazelwood, MO 63042

---------------------------------------------------------------------------------
DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF DesignerCouncil.
To temporarily stop/(restart) delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL/(MAIL)
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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
---------------------------------------------------------------------------------

---------------------------------------------------------------------------------
DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF DesignerCouncil.
To temporarily stop/(restart) delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL/(MAIL)
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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
---------------------------------------------------------------------------------