Brown Oxide Treatment (BOT)
Brown oxide treatment is a generic term to describe a chemical process applied to copper lead frame as adhesion promoter. This treatment was originally developed for enhancing adhesion between copper circuity and laminated material in PCB substrate. However, field evaluations reported that the typical process recommended by chemical suppliers did improve adhesion but at the same time deteriorating the wire bonding performance, specifically non-stick-on-lead (NSOL). Our chemical experts were called for a solution and finally developed a modified brown oxide treatment fitting for lead frame application: on one hand improving its adhesion to Encapsulation Molding Compound (EMC); while on the other hand ensuring no deterioration on wire bonding performance. This lead frame BOT uses both mechanical and chemical mechanisms to enhance its adhesion with encapsulation molding compound (EMC), with quantitative measure of Brown Oxide thickness at angstrom scale.
In recent years, the demand for QFNs has been increasing. One of the features of QFN is that it has exposed bottom terminals and DAP that are soldered directly onto printed circuit board by Surface Mount Technology (SMT). If the surface of the lead frame is roughened, it is relatively prone to the risk of EMC mold flash issue and consequently affect the quality of the surface mount. In response to the needs of some customers, we provide two different single-sided BOT solutions for QFN lead frames: (1) Using the original attached lead frame backside polyimide tape as a protective film to block its contact with BOT chemicals, so as to create a single-sided (top and lateral side) BOT effect; (2) The use of special protective film in par with adjustment of the BOT process, it can also create a single-sided BOT treatment without the use of backside polyimide tape.
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