SMT007 Magazine

SMT007-Sept2020

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98 SMT007 MAGAZINE I SEPTEMBER 2020 As electronic passive components continue to shrink in size, methods for their rework need to be developed by electronic manufacturers to maintain and support PCB assembly pro- cesses. The 0201 package—only 20 by 10 thou- sands of an inch in size—is one of the compo- nents requiring a higher degree of rework skill compared to other larger packages. IPC-7711 and IPC-7721 on the "Rework, Modification, and Repair of Electronic Assem- blies" [1] for these resistor and capacitor sizes out- lines a variety of meth- ods in sections 3.3.X. Here, I will compare and out- line a few of these rework methods. While the 0201 package size has been in the main- stream for several years, assembly soldering defects are common. Tombstone defects, common for this package type, are commonly caused by the pads heating up at different rates. A thermal mass imbalance may cause one of the pads to heat at a dif- ferent rate compared to the other. For exam- ple, if one of the 0201 pads is connected to a thermal ground plane and the other pad is not, the unconnected pad will heat at a faster rate—all others being equal. This thermal imbalance will cause the tombstoning defect as the molten solder pushes up one side of the component. It is well understood that lighter and smaller components are more susceptible to this tomb- stoning phenomenon. A similar result is real- ized if the pads are not the same size, as the larger pad will heat at a slower rate. The pad sizes influence the defect rate; smaller pad sizes result in higher defect rates [2] . The com- ponent placement offsets in the X and Y direction are one of the larg- est contributors to the post- reflow defect rates of these packages. This means that t h e a s s e m b l e r needs to control these parameters by placement con- sistency through p ro p e r p l a c e - ment program- m i n g , n o z z l e maintenance, and place- ment pressure. In addi- tion, the very small pad geometries of the 0201 pack- ages make solder paste printing consistency a challenge, which can also cause defects. A Conductive Soldering Rework Technique The most common technique used to remove and replace 0201 body style components is through the use of a conductive hand solder- ing system. This hand soldering rework tech- nique calls for the removal of a passive com- ponent by employing a micro body tweezer or a micro hoof soldering tip. For part removal using a micro hoof tip, make sure to first tin PCB Rework of 0201 Packages Knocking Down the Bone Pile by Bob Wettermann, BEST INC.

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