You can check also the symmetric thickness and materials in z axis to the center line Best Regards Reuven ROKAH e mail: [log in to unmask] Think green before printing this mail... Thanks -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Herminia Guevarra Sent: Monday, September 08, 2008 4:04 PM To: [log in to unmask] Subject: Re: [TN] Bow and Twist Measrement - [(Could Be SPAM- Header Check)] Email has different SMTP TO: and MIME TO: fields in the email addresses Just had a recent bow issue and PCB vendor cited root causes were unbalance copper residual between left and right side dummy and unbalance pressure distribution in lamination process. A PCB may appear to have a slight bow prior to reflow, and will have a progressively greater bow after each assembly reflow cycle. FYI. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo Sent: Monday, September 08, 2008 8:44 AM To: [log in to unmask] Subject: Re: [TN] Bow and Twist Measrement - [(Could Be SPAM- Header Check)] Email has different SMTP TO: and MIME TO: fields in the email addresses Bow and twist in excess spec normally indicated either poor design .l unbalenced layout, or poor qual of Mfg, or both. -------------------------- Sent using BlackBerry ----- Original Message ----- From: TechNet <[log in to unmask]> To: [log in to unmask] <[log in to unmask]> Sent: Mon Sep 08 06:00:09 2008 Subject: Re: [TN] Bow and Twist Measrement Though IPC 610D sections 10.2.7 mentioned acceptable for class 1, 2 and 3 as long it does not cause damage during post solder assembly operations or end use. Consider "form, fit and function" and product reliability. Only IPC 600 (raw PCB) mentioned it is not acceptable. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Rex Waygood Sent: Monday, 8 September 2008 4:21 PM To: [log in to unmask] Subject: Re: [TN] Bow and Twist Measrement I agree A lot of machines won't cope with the bow and twist permitted in the standard. Rex Rex Waygood Technical Manager PartnerTech Poole Ltd Benson Road Poole Dorset BH17 0RY United Kingdom Tel: +44 (0)1202 674333 Fax: +44 (0)1202 678028 DDI: +44 (0)1202 338222 Mob: +44 (0)7887 997403 [log in to unmask] www.PartnerTech.co.uk -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Genny Gibbard Sent: 05 September 2008 18:58 To: [log in to unmask] Subject: Re: [TN] Bow and Twist Measrement The tighter one. Surface mt. You need to gear it to the component most susceptible to damage from Warp/Twist -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Paymon Sani Sent: September 5, 2008 11:53 AM To: [log in to unmask] Subject: [TN] Bow and Twist Measrement Hello All, IPC-A-610 Rev. D, Section 10.2.7 allows 1.5% and 0.75% Bow and Twist for Through-hole and surface mount assemblies accordingly. What percentage should I be applying if the assembly has mixture of surface mount and through-hole components? 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