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 Actually, RB-276 has been superceded by IPC-6011 and 6012.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. ################################################################ 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. 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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 ################################################################