Moisture entrapped in the PCB and/or components could be the reason for solder balling.
1 variable at a time - Hand-solder to a bare PCB pad and check for solder balls. Repeat the test with components on the PCB.
As an additional test, the board and components can be baked for 125 deg C for 4 hours to remove entrapped moisture- and then hand-soldered.
Karthik Vijay
Technical Manager - Europe
Indium Corp.
Currently with Indium Corporation and responsible for technology programs and technical support for customers in Europe. Over 15 yrs experience in SMT, Power, Thermal & Semiconductor Applications. Masters Degree in Industrial Engg, State University of New York-Binghamton.
You don't mention if you are using solder wire or solder paste for your 8 lead SMT components.
If you are using solder wire, you might need to increase the activity of your flux to better clean the pads or component leads during the soldering process. You should also reduce the tip temperature of your soldering iron.
If you are using solder paste, your soldering iron is heating the solder paste too fast causing the solder to separate and ball up. Try a hot air tool, it will heat the assembly slower allowing the flux to activate and reducing the possibility of solder balls forming.
Edward Zamborsky
Regional Sales Manager
OK International Inc.
Ed Zamborsky is a Regional Sales & Technical Support Manager for Thermaltronics, located in New York. His position requires frequent customer visits throughout North America and the Caribbean and his position encompasses not only sales but the role of trainer and master applications engineer for all of Thermaltronics products. His expertise includes such specialties as hand soldering, convection and conduction reflow techniques, array rework, fluid dispensing equipment, and fume extraction. Ed has authored many articles and has presented many papers on topics such as; Low Volume SMT Assembly, Solder Fume Extraction, SMT Rework, BGA Rework, Lead-Free Hand Soldering, High Thermal Demand Hand Soldering, Lead Free Visual Inspection and Lead Free Array Rework.
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