I just looked up the applicable specs. IPC 6012 states that: "The
printed board shall have a maximum bow and twist of 0.75% for boards
that use surface mount components and 1.5% for all other boards." IPC
-A-600E states: "The entire portion of the specimen or production board
shall have a maximum bow and twist of 1.5%, unless otherwise specified
on the master drawing. For automated assembly and surface mounting
requirements, more stringent requirements may be necessary." IPC-A-610B
and J-STD-001 for assembled boards state: "Bow and twist after soldering
shall not exceed 1.5% for through-hole and .75% for surface mount."
Mary Muller
Materials and Processes
ELDEC Corp.
Lynnwood, WA
> ----------
> From: Mitch Morey[SMTP:[log in to unmask]]
> Reply To: TechNet E-Mail Forum.;Mitch Morey
> Sent: Thursday, February 19, 1998 9:17 AM
> To: [log in to unmask]
> Subject: Re: [TN] PCB warpage - Reply
>
> Daniel,
>
> Unless it's been updated in the amendment to IPC-RB-276, both
> IPC-D-275 and RB-276 call out for bow and twist (flatness) to
> be 1.5% of the overall feature. IPC-D-275 is a design guidelines
> spec, the RB-276 is the qualification spec, so wouldn't you
> actually be more concerned with the RB-276 specification.
>
> Actually, RB-276 has been superceded by IPC-6011 and 6012.
> I don't have those specs yet, but I don't see that general requirement
> changing.
>
> Any help?
> L8r, Mitch Morey
>
> >>> "Shea, Daniel" <[log in to unmask]> 02/19/98 03:52am >>>
> 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.
>
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