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Page 102 of 119

AUGUST 2019 I PCB007 MAGAZINE 103 Things to Watch for During UV Bump In some cases, UV bump might degrade the adhesion of legend ink or conformal coating. This depends on the product formulation. Af- ter curing of the solder mask, you have active molecule centers left. These active centers contribute to good ad- hesion of legend ink and conformal coating. During UV bump, these active centers are be- ing destroyed, giving bad adhesion. This phe- nomenon depends on the type of legend ink and conformal coating. Some products are more prone to adhesion loss than others. To prevent wrinkling of solder mask between tracks at high copper height and high SM de- posit, UV bump before thermal cure is helpful and recommended. Staining of the solder mask after HASL can be prevented by giving boards a UV bump cure after the final thermal cure. This staining is caused by aggressive fluxes and washing the boards whilst still hot. This hap - pens mainly when exposure is direct imaging and is due to the missing wavelength of 200– 350 nm. The solder mask surface is not sealed. Direct Imaging If you process solder mask on contact-expos- ing units with UV light-emitting diodes as the light source, or direct imaging systems with UV light-emitting diodes or UV laser-emitting di- odes, then consider UV bump before final ther- mal cure, as it improves the staining resistance to final finishes. Other Applications UV bump is widely used in other applica- tions as well. UV bump is also used for curing UV legend ink, UV solder mask, UV etch resist, UV gap filler, and UV hole filler. All of these products have been developed for UV curing. Thermal curing of these products is not pos- sible. Most solder mask manufacturers have such products in their portfolio. Apart from the PCB industry, UV bump is also used in other industries for curing of inks, paints, resins, etc. Some companies do not have UV bump and get along well without. But if UV bump is used and needed, the energy must be monitored very carefully because it drifts away. PCB007 References 1. Technical datasheets from Taiyo, Huntsman, Sun Chemical, and Lackwerke Peters. Nikolaus Schubkegel retired in Feb- ruary 2019. For the past 12 years, Schubkegel worked at Umicore Gal- vanotechnik GmbH in Germany as a technical service engineer for Taiyo products. Before that, he worked as a process engineer in the solder mask department at the former IBM-PCB plant (later STP) in Albstadt, Germany. Schubkegel obtained an M.Sc. degree in chemical engineering from the Polytechnic Institute in Timisoara. Oak Ridge National Laboratory (ORNL) is training next-generation cameras called dynamic vision sensors (DVS) to interpret live in- formaion—a capability that has applications in robotics and could improve autonomous vehicle sensing. Unlike a traditional digital camera, a DVS transmits per-pixel changes in light intensity. Individual pixel locations are recorded and time-stamped to the microsecond, creating data "events" that are processed by a neuromorphic network—a type of intelligent, energy- efficient computing architecture. This capability makes the sensors fast, power-efficient, and effective in wide ranges of light intensity. "Because the DVS records only changes in what it sees, there is no redundant data," said ORNL SULI intern Kemal Fidan. (Source: ORNL) 'Seeing' in Real Time

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