Hello,
Based on my experience, PCB manufacturers don't give this data. I have
found the susceptibility for warping depends on the size of the bare board,
layer count, and copper weight. I have very large dense backplanes and
midplanes with double sided SMT and wave, and they don't warp, twist or
deform at all. (They also take 2 men and a boy to lift!) I also have very
thin cards with .031 substrates which are warped from the manufacturer
before I do anything to them. So we fixture them to prevent the condtion
from worsening.
What you need to do is to examine the boards as they arrive from your
supplier. Lay them out on a flat surface, granite is nice, and use a dial
indicator to measure the deflection. Serialize the boards, run them through
the process, repeating the measurements after every heat cycle. Then you
will be able to determine if your process is causing the warping.
The only other piece of advice I can offer is to cool the boards on a flat
surface. Don't put them onto a vertical or slanted rack until they are
cool.
I hope this helps you,
Wendy Casker
-----Original Message-----
From: Tempea, Ioan <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Friday, May 21, 1999 2:00 PM
Subject: [TN] PCB specs
>Hi PCB fabs,
>
>this one's for you.
>
>I'm caught into a lot of fussing about whether my reflowing profiles warp
>the boards or not.
>
>What I'd like to know is if the PCB manufacturers recommend optimal reflow
>profiles for their boards or, at least, two things:
>
>1. maximum temperatures the boards can withstand without warping or getting
>damaged in any way
>2. maximum number of thermal cycles the board can take, including double
>reflow, waving and some rework
>
>I don't mind if I hear from PCB users either.
>
>Have a good week-end after answering, Ioan
>
>################################################################
>TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
>################################################################
>To subscribe/unsubscribe, send a message to [log in to unmask] with following
text in the body:
>To subscribe: SUBSCRIBE TechNet <your full name>
>To unsubscribe: SIGNOFF TechNet
>################################################################
>Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section
for additional information.
>For technical support contact Hugo Scaramuzza at [log in to unmask] or
847-509-9700 ext.312
>################################################################
>
>
################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe: SUBSCRIBE TechNet <your full name>
To unsubscribe: SIGNOFF TechNet
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################
################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe: SUBSCRIBE TechNet <your full name>
To unsubscribe: SIGNOFF TechNet
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################
|
