IPC-6012 "Qualification and Performance Specification for Rigid Printed Boards"
Section 3.4.4 Bow and Twist
"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. Panels which contain multiple
printed boards which are assembled on the panel and later separated SHALL be assessed
in panel form.
Bow, twist, or any combination thereof, SHALL be determined by physical measurement
and percentage calculation in accordance with IPC-TM-650, Method 2.4.22, which
describes four procedures to determine bow and twist of either cut to size panels or
finished rigid printed boards including single-sided, double-sided and multilayer."
IPC-6011 "Generic Performance Specification for Printed Boards" Section 1.4
Interpretation
"SHALL, the emphatic form of the verb, is used throughout this specification whenever
a requirement is intended to express a provision that is binding. Deviation from a
SHALL requirement may be considered if sufficient data is supplied to justify the
exception. . ."
ANSI/J-STD-001B "Requirements for Soldered Electrical and Electronic Assemblies"
Section 9.2.3 Bow and Twist (Warpage)
"Bow and twist after soldering should not exceed 1.5% for through-hole, or 0.75% for
surface mount printed board applications (see IPC-TM-659, 2.4.22). Bow and twist MUST
not cause damage during post solder assembly operations or use."
J-STD-001B Section 1.4 Definition of Requirements
"When the word MUST is used the requirements are mandatory for all product classes.
When the word SHALL is used, the requirement is mandatory only for Class 3 products.
. ."
Jack Crawford, IPC Project Manger - Assembly
2215 Sanders Road, Northbrook IL 60062-6135
[log in to unmask] http://www.ipc.org
847-509-9700 x 393
fax 847-509-9798
>>> Mitch Morey <[log in to unmask]> 02/19/98 11:17AM >>>
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Actually, RB-276 has been superceded by IPC-6011 and 6012.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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