Brad,
Here's a note that I use on my fabrication drawings...
"BOW AND TWIST SHALL NOT EXCEED 0.75% (.0075 IN PER IN) IN ACCORDANCE WITH
IPC-A-600 FOR SURFACE MOUNTED BOARDS WHEN MEASURED USING IPC-TM-650, METHOD
2.4.22."
If you are doing thru hole technology you can relax that requirement to 1.5%
(.0150 IN PER IN)
Most surface mount assembly vendors like to have a very flat surface upon
which to place components... the uniformity of the thickness and shape of
the solder paste printed on the lands is affected by how well the paste
screen mates with the surface of the board too. Obviously the paste will
bleed out under the screen opening edges loosing its shape definition if the
screen is not right on the surface of the board. Also controlling the
uniform height above the surface of the board affects the difficulty in
programming the pick and place machines and handling the parts in pick and
place... they need to locate the part in the X,Y and Z planes and if the
board isn't flat they can be pushing the part too hard onto the surface or
not close enough... Sometimes they can clamp the board in tooling fixtures
or heat the boards under pressure to flatten them and compensate somewhat
for poor bow and twist if it isn't too severe but the best way to control it
is through good design practice. Use of evenly distributed copper areas and
symmetrical layer stack up in your design helps a lot.
I hope that helps a little...
Best regards,
Bill Brooks
PCB Design Engineer, C.I.D.+
www.pcbwizards.com
-----Original Message-----
From: Stephen Chavez [mailto:[log in to unmask]]
Sent: Tuesday, June 13, 2006 4:42 PM
To: [log in to unmask]
Subject: Re: [DC] PCB warpage tolerances
Brad,
I think it's the following:
"Warp or twist of board shall not exceed .010 inch per inch"
I'd like to see other responses on this issue.
Regards,
Stephen V. Chavez
Vista Systems
602-943-5700
www.vistasystems.net
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
Jaurique, Brad
Sent: Tuesday, June 13, 2006 4:35 PM
To: [log in to unmask]
Subject: [DC] PCB warpage tolerances
All,
We have a design that sits in a mechanical
housing that has crevices and milled out areas. Due
to this the standoffs are different heights and sizes.
There are of course mechanical tolerances with these.
My question is what is the IPC standard for pcb warpage tolerances. My
assembly department is telling me that we don't meet these standards yet
can't define what they are.
All help is appreciated.
Brad Jaurique C.I.D.
Senior PCB Designer
Pelco
Office - (559)292-1981 ext. 2347
Cell - (559)940-3966
[log in to unmask]
Tell me and I forget; Show me and I remember; Involve me and I understand.
================
Confidentiality Note:
The information contained in this transmission is legally privileged and
confidential, intended only for the use of the individual or entity named
above. If the reader of this message is not the intended recipient, you are
hereby notified that any dissemination, distribution, or copying of this
communication is strictly prohibited. If you receive this communication in
error, please delete the message and notify us immediately by telephone call
to +1-559-292-1981.
================
---------------------------------------------------------------------------------
DesignerCouncil 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 DesignerCouncil.
To temporarily stop/(restart) delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL/(MAIL)
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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
---------------------------------------------------------------------------------
|
