Wee Mei,
what is the moisture absorption rate of your board? Did you do a wash prior
to assembly? Why you need 60C at 30 min? Did you change the vendor of your
board (different from the 60C 30 min process qualification days)? 2 cm is a
a BIG delam. Did you use the board for eutectic and just changed over to
leadfree (20-40 degree higher reflow)?
jk
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Dehoyos, Ramon
Sent: Friday, October 08, 2004 9:30 AM
To: [log in to unmask]
Subject: Re: [TN] Baking Temp and Time
Hi Wee Mei:
From experience and a lot of technetters inputs in this forum FR4
does not need to be baked under normal conditions. Either there is a problem
with the fabrication of the board, there was some mechanical stress induced
such as riveting or the reflow temp is too high or for too long period of
time.
Regards,
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Lum Wee Mei
Sent: Friday, October 08, 2004 12:03 AM
To: [log in to unmask]
Subject: [TN] Baking Temp and Time
Hello,
We used to bake our bare boards prior to assembly at 60 degree C for 30min.
Recently, several mounted boards have delamination surfacing. One of them
has
interesting fact that the delaminations are noticed when the inspector is
checking the fully populated board.
For these boards, the bare boards are baked at 60C for 30min and have BGAs
reflow. The rest of the components are manually assembled 1 day later.
However,
the operator did not flag up any delamination until the QC inspector spotted
them when inspecting the fully mounted boards. The delaminations as big as
2cm
in diameter at several locations but at around pads.
I scan through IPC-HDBK-001 and it recommend 3 baking temp and time :
(a) 80C for 18 - 48hrs
(b) 100C for 8 - 16hrs
(c) 120C for 3.5 - 7hr
As our schedule is always very tight, I was told to take (c). My concerns
are :
(1) Isn't it that (c) is too near the Tg of the laminate and will have
impact?
(2) I interpret the above 3 requirement to be applicable during fabrication
process and not prior to assembly. Pls correct me if I mis-interpret.
On the other hand, I also come across IPC-PE-740 that recommends otherwise
for
moisture and volatile removal : 100 - 125C for 2-4hrs.
Now,which temp and time should I adopt prior assembly as both temp in 001
and
740 are close to the laminate Tg (FR4).
For expert opinions will be greatly appreciated.
Regards,
Wee Mei
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