Carl
You got the 120C number from Table 4-1 in IPC-2222, right? What's the minimum dielectric thickness in the board? It's also important to note that this chart just lists FR4 and doesn't have a separate listing for Higher Tg materials. I think this is why they include footnote 6 "Other materials in the same classification with higher operating temperatures may be available." You want to avoid low Tg FR4 materials since you'll be very close to that transition point. The best thing to do is find out from the laminate manufacturer what the maximum continuous operating temperature for their material is. This information is not usually on the standard data sheets but it is available.
One other thing you need to watch out for is to make sure you're fabricator has UL recognition for high enough Maximum Operating Temperature (MOT) for the materials used in this board. It's not enough to ask for flammability. You also need to specify a specific MOT if you want it and you probably want at least 130C for this board.
Mike McMaster
RF Product Engineer
Merix Corporation
503-992-4263
----------
From: Carl VanWormer[SMTP:[log in to unmask]]
Reply To: TechNet E-Mail Forum.;Carl VanWormer
Sent: Tuesday, May 13, 2003 2:10 PM
To: [log in to unmask]
Subject: [TN] Hot Boards!
I have some FETs soldered to exposed surfaces on my board (D-squared
package). Under some conditions, they may get up around 120C (the part is
rated up to 175C). I'm not worried about the FET, but I may be playing with
fire on the board. I want to know how much fire I'm playing with . . .
The IPC maximum temperature spec for FR-4 is 120C (if I'm reading things
correctly). What type of things start to happen at this temperature? Is
this where the board starts to discolor over time, or are there physical and
electrical changes that occur in this range. Do I need to worry about long
term reliability?
Thanks,
Carl
Carl Van Wormer
Cipher Systems
1815 NW 169th Place, Suite 5010
Beaverton, OR 97006
Phone (503)-617-7447 Fax (503)-617-6550
---------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8e
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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/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
-----------------------------------------------------