Hey guys,
There are many reasons why there are different laminate materials. I
leave the science to your engineers in the actual selection of
materials.
What I can tell you, is LF BGA rework will discolor, and in most cases
completely destroy ANY PCB with a DECOMPOSITION (Td) < 330 Degrees C.
I've seen no visible signs of destruction when the Tg (of the Td >330 C
boards) was at 145.
Most of the higher Td boards also have Tg >150, so you should do your
own stress testing to see which material you like or need.
There are new materials coming out to meet the cost requirements of
those of us in competitive markets, we are watching closely but expect
our laminate will be Tg< 155 C.
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of MA/NY DDave
Sent: Tuesday, March 08, 2005 8:24 AM
To: [log in to unmask]
Subject: Re: [LF] Tg-Td
Hi Dennis, Dewey, G, W, IPC LF Listservers
<Because moving towards higher Tg increases the costs of the PCBs, where
<ever possible I would have liked to not change the laminate.
As I have wrote before, this is possible yet you have to know your
entire
product which includes processing, usage, servicability, reliability.
<Having different spec PCBs would also cause confusion with our
purchasing
<& IQA departments and/or our customers (who supply the PCB specs). Some
<may not be aware of the implications of higher processing temperatures
and
<rely on us to provide this expertise.
Absolutely I agree. You are the OEM, You are the GOD, customer, and can
not
delegate that to a subordinate. Some do to First Tier EMS suppliers yet
they do themselves and their customers a great disservice.
<Therefore if there was a general rule, which perhaps could be "up to
<6layers, FR4 Tg140C is sufficient, all else use Tg170C or greater", it
<provides a good guideline, and would ultimately help us and our
<customers ensure a reliable product.
ANYONE who suggests to you without knowing your product, materials,
components, life expectancy i.e. "materials, methods, men, management,
more" would be WRONG and you will pay in "end games"
You have to find out for your current product how close you are now to
the
limits of what you are guaranteeing to your customers. Hire a
Reliability
Engineer, or a Good Product Engineer and set them free.
BTW our buddy Honeywell-Dewey gave a good answer, I knew we could could
on
him for more than humour.
Yours in Engineering, Dave
Y i Engr, MA/NY DDave
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Search previous postings 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
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