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94 SMT007 MAGAZINE I MARCH 2021 e part or board label may need to be masked with Kapton™ or liquid mask to prevent the markings from disappearing during processing. Other Operations ere are several operations on the com- ponents themselves which need to be consid- ered. Small legged leads such as high pin count QFPs may need to have their leads straight- ened and formed to be coplanar upon removal to meet the JEDEC requirements so that they can be placed correctly onto a potentially new PCB. Solder balls will need to be re-attached to a removed BGA or CSP through a re-balling process to place it onto a new assembly. Part datasheets will help determine the correct ball size. Customer order details will determine the correct solder alloy. For part salvaging, be careful of the maxi- mum temperature the components can with- stand. is will be important to understand as the right removal process tool and pro- file needs to be chosen. Proper profiling will ensure that the temperature limits of the component are maintained during the removal process. Coatings Not only should the MSL of the components be considered, but it should be noted whether the boards have been conformally coated, have had components staked in place, or underfill applied to the components. e presence of underfill or conformal coating on and under- neath the components to be removed is sig- nificant as there are numerous stripping pro- cesses which can be employed as part of the removal operation. In some cases, this may cause difficulties, including throughput issues. It is important to determine the overall area of conformal coating removal at the onset. For example, if conformal coating needs to be removed from the component body, this pro- cess may have the unintended consequence of part number, date code, and other information being removed from the package. Adhesives and underfills may soen during removal but their later removal from the com- ponent body may take too much time to make the salvaging economically feasible. In addition to the above items, the electrostatic discharge (ESD) sensitivity level of the component should also be considered during the salvaging process. Just because the parts are being salvaged doesn't mean that they should not be handled like "live" boards. e compo- nent datasheet will inform the remover of the type of ESD precaution that needs to be taken. Labels Another area of concern is the label on the compo- nent or the PCB. All the sal- vaging processes—includ- ing the conformal coating stripper, heat, cleaner and flux—will interact with the board where compo- nents are to be salvaged. Figure 2: Re-balled BGA marking after salvaging.

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