Hi, Nancy,
I don't think your questions can be answered as simply as you would like,
so I offer the following:
Q1 - (a) & (c) - we couple up to 6 points depending on the board and its
contents. For BGA's (1.27mm pitch), for example, we drill through the
underside of the board into a central ball and bond a TC there with
conductive epoxy. For Gull wings, we TC the solder joints on the board
surface. No point in putting TC's on top of a component unless case max
temp is critical. Attachment to a component surface is done using aluminium
tape.
Q2 - (a) & (b) For eutectic solders (183 deg C liquidous), we go for a
profile that gives us overall a soldering temperature of liquidous + 20 deg
C. It's based on the profile given by the soldering manufacturer and
adjusted as required to meet board conditions. With higher melting point
solders (210 deg C), there is a ceiling temperature for most active
components that should not be exceeded, or they fall apart inside. The
delta between solder liquidous + 20 deg C and the ceiling temp therefore
becomes very small, disappears altogether or becomes negative (in which
case you have a problem, Houston).
Q3 - (a). We run a board, set up with TC's for profiling, through the oven
and adjust the peak temp and duration until all components are at liquidous
+ 20 at their joints, but not exceeding their max case temps. i.e. if some
components are getting too hot before others are up to temp, we reduce the
peak temp and increase the duration of exposure. We normally use 63/37
solder with a paste formulation used for fibre optics boards. Works for us.
Hope this helps you some.
Peter Duncan
Nancy
Reynolds/MKT/HQ To: [log in to unmask]
/KEMET/US cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST
<NancyReynolds@ Aero/ST Group)
KEMET.COM> Subject: [TN] Reflow Process Profiling Methods
Sent by:
TechNet
<[log in to unmask]
G>
11/09/01 04:25
AM
Please respond
to "TechNet
E-Mail Forum."
Hi Technet,
I need some help to identify the most common methods of thermocouple
placement when profiling reflow processes. And while we are on the
subject, I would also like to collect information on targeting for typical
or recommended profiles versus absolute min/max boundaries. Just three
easy multiple choice questions....
1. Where do you put the thermocouple?
a. Embedded in a solder joint?
b. On top surface of a component? (If so - how do you attach the TC to
the part?)
c. On surface of the PWB?
d. In air?
2. Do you target reflow profiles to fit a "typical" curve or do you just
try to stay below a maximum?
a. Target for typical?
b. Stay below maximum?
3. How do you specify that Typical or Maximum condition?
a. Peak Temperature and Maximum Time at that Peak? (Please define
conditions.)
b. Total time above a fixed value (usually 183 $B!k (BC or 200 $B!k (BC)? (Please
define conditions.)
c. Solder Paste Alloy composition for above values? (If you are running
both SnPb and Pb-free, please reply for both)
If any of you would like to share soft copies of actual time/temp profiles
that you use for targeting or specifying an acceptable range of reflow,
please email to me off-line.
Thanks in advance for your help.
Nancy Reynolds
KEMET Electronics
---------------------------------------------------------------------------------
Technet 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 Technet
To temporarily halt delivery of Technet send the following message: SET
Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases >
E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
ext.5315
---------------------------------------------------------------------------------
[This e-mail is confidential and may also be privileged. If you are not the
intended recipient, please delete it and notify us immediately; you should
not copy or use it for any purpose, nor disclose its contents to any other
person. Thank you.]
---------------------------------------------------------------------------------
Technet 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 Technet
To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------
|
