Daniel,
We specify maximum bow and twist for a panel (or an individual board if
it comes to us that way) to be 0.3%. We don't generally have the
problem of receiving boards that do not meet this specification. I am
not aware of any price premium being imposed because of this
requirement.
Steven Lustig
Process Engineer
EMS Technologies
Norcross, GA
[log in to unmask]
>----------
>From: Shea, Daniel[SMTP:[log in to unmask]]
>Sent: Thursday, February 19, 1998 6:52 AM
>To: [log in to unmask]
>Subject: Re: [TN] PCB warpage -Reply
>
>Matthew,
>
>IPC 275 specs out a multilayer .060" thick board as having a flatness
>requirement of 1% which equates to .010" / inch.
>
>Most of the time we receive boards that are well within the spec and we
>process them with no difficulty. When an occasional lot of boards are
>received that are on the high side of the spec we experience all the
>problems you described.
>
>Do you specify a tighter tolerance with your pwb shop. Does this tighter
>spec cause an increase in pwb cost. ( According to IPC to reduce the spec
>to .5% or .005" / inch reduces yields.
>
>I am curious as to what you and the majority of the industry is
>specifying.
>
>Thanks,
>
>Dan Shea
>Sr. Manufacturing Engineer
>The Foxboro Company
>Tel # 508-549-2410
>Fax # 508-549-4379
>Email: [log in to unmask]
>
>
>-----Original Message-----
>From: Matthew Park [SMTP:[log in to unmask]]
>Sent: Wednesday, February 18, 1998 6:53 PM
>To: [log in to unmask]
>Subject: Re: [TN] PCB warpage -Reply
>
>JIm,
>
>By the look of your message, you must be a quality eng/mgr or
>sales eng/mgr. No harm if i am wrong. Qual/'sales eng/mgr's
>usually like to go by the book and process/mfg eng's like to go by
>what work and what not work. To get to my points, IPC-275 Bow
>& Twist spec should be in a permanent storage. Boards that
>are closer to 0.01"/inch spec causes some problems in smt
>manufacuring and th wavesolding.
>
>They introduces printing registration inaccuracies, uneven
>solderpaste depositions and solderpaste skips. They go thru
>bumping rides during p/p placement cycles and off-placements
>of plcc's, qfp's and bga's are visible. They wont transfer thru
>edge conveyors without an operator assistence. Some chip
>components get disloged due to the springness of boards and
>slight vibrations. They cause more open solder joints.
>
>They allow flooding of solder on comp side during
>wavesoldering and prevents solder wetting on the highest area
>of warped boards. It becomes more important to have flat
>boards with advancement of finer qfp's and bga's.
>
>Bow & Twist spec of 0.002"/inch or less is better suitable for SMT
>assy. I know a lot of board fab shops won't guarantee with hasl
>boards.
>
>regards
>Matthew Park
>Automation Engineer
>NII Norsat International Inc.
>
>>>> Jim Mathis <[log in to unmask]> February 18, 1998 2:27
>pm >>>
>I spec'd out .01"/inch, also, which used to be the spec. IPC-275
>section
>5.2.5.2 now specs Bow & Twist in terms of percentages. If you
>don't have a
>copy of IPC-275, let me know and I'll fax you the appropriate
>pages.
>
>################################################################
>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 web site (http://jefry.ipc.org/forum.htm) for
>additional information.
>For the technical support contact Dmitriy Sklyar at
>[log in to unmask] or 847-509-9700 ext.311
>################################################################
>
>################################################################
>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 web site (http://jefry.ipc.org/forum.htm) for additional
>information.
>For the technical support contact Dmitriy Sklyar at [log in to unmask] or
>847-509-9700 ext.311
>################################################################
>
>################################################################
>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 web site (http://jefry.ipc.org/forum.htm) for additional
>information.
>For the technical support contact Dmitriy Sklyar at [log in to unmask] or
>847-509-9700 ext.311
>################################################################
>
>
################################################################
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 web site (http://jefry.ipc.org/forum.htm) for additional information.
For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311
################################################################
|
