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March, 2021 Continued from previous page


good, and become another kind of challenge. Chip soldering, for example, is charac-


terized by the shape of the resulting menis- cus. The height of the solder is a measure of quality. Under nitrogen, the observed wet- ting height may be lower than in air — mean- ing the non-wetted area (gap) increases. The reason for this is actually the


improved spreading of solder under nitrogen. Since the solder has to work against gravity to wet the component connection, the pad is wetted more easily. In addition, the sphere height is lower when there is greater spread- ing, and as a result, there is less solder avail- able to rise at the component connection.


Tombstones are caused by dif- ferences in wetting time from one end of a component to the other. If one of the solder joints melts before the other, the wetting forces and surface tension of the liquid will cause the other end of the component to rise upward, away from the substrate. This renders the second solder joint useless. Under a nitrogen atmos-


phere, it is often reported that reflow soldering results in more tombstone defects. The reason is again the improved wetting, which usually increases the time difference between the two com- ponent connections.


Balancing Pros and Cons A specialist in thermal sys-


tem solutions, such as Rehm, can help customers to understand the


Building Resilience into High-Mix Electronics Manufacturing


Continued from page 49


pany has reported a 300 percent increase in capacity, using less floor space than the previous machines. Parker’s estimated pro-


gramming time has been cut by 80 percent and its placement component range has been expanded by 50 percent. The company hopes to standardize other facilities on a common plat- form for economies of scale, ease of production redeployment and to keep personnel familiar with the equipment. ASM’s technology suite has


helped Parker lay the foundation for a resilient operation able to manage dynamically changing products, a global pandemic and the acceleration of technological requirements. Contact: ASM Assembly


Systems, 3975 Lakefield Court, Suite 106, Suwanee, GA 30024 % 770-797-3189 E-mail: ogden.mark@asmpt.com Web: www.asm-smt.com r


See at IPC APEX (virtual)


Analysis of a head-in-pillow defect in a BGA ball, which can be caused by surface oxidation or poor wetting during reflow.


www.us-tech.com


Page 55 The Effects of Reflow Soldering in Nitrogen on Defects


benefits and potential drawbacks of new process technology. This kind of expertise is invaluable, as the investment in advanced technology can be wasted if fundamental properties of the materials are not consid- ered.


Rehm manufactures reflow soldering


systems that use convection, condensation and vacuum, as well as drying and coating systems, functional test systems, equipment for the metallization of solar cells, and cus- tom machines. Contact: Rehm Thermal Systems, LLC,


3080 Northfield Place, Suite 109, Roswell, GA 30076 % 770-442-8913 E-mail: c.kramer@rehm-group.com Web: www.rehm-group.com r


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