Standard of PCB Bow and Twist in Incoming Inspecion| 27 February, 2003
Hi all, We got some bare pwb in our incoming inspecion looked really wrapped. The maximum twist of the pwb we messured is 0.056inch by following the method in IPC-TM-650 2.4.22 C. (The diagonal size of our pwb is 7.5inch) According to the IPC standard: R=2(D)(T)/100=2*7.5*0.75/100=0.1125inch. One tenth inch of twist seems very big for the smt process. Can anybody tell me how to setup a standard for bare pwb incoming inspection? Appreciate your help.
Standard of PCB Bow and Twist in Incoming Inspecion| 28 February, 2003
Without drilling through the numbers, they're probably correct. Recognize that standard warp / twist specs [IPC-A-610 1.5% for PTH only and 0.75% for SMT] are not going to make it on tech boards. You need to define specific requirements.
This warpage problem is driven by: * MLB constructions (not homogeneous or unbalanced - too resin rich or poor) * Poor supplier process capabilities (lamination cycles) * Poor material selections (usually cheap and dirty), etc.