Authored By:
Frank Xu Ph.D., John Fudala, Michael Orsini, Robert Farrell, Martin Bunce
MacDermid Alpha Electronic Solutions
Haley Reid
KYZEN Corporation
TN, USA
Summary
When it comes to successful soldering, Organic Solderability Preservative (OSP) coatings play a crucial role, especially in the packaging arena. To ensure reliability, it is important to understand all the factors that influence OSP performance and durability throughout the entire fabrication and assembly process.
OSP process selection is crucial. The organic molecule must provide a coating of sufficient thickness and thermal stability to provide suitable shelf life from the time of OSP application through the first reflow process. Also, the coating must have resistance to the de-flux cleaning chemistry, and compatibility with the final assembly process, and materials, to consistently ensure high yields.
OSP and assembly processing has been thoroughly characterized over the years, but interaction with the de-flux cleaning chemistries is less well understood. To better understand OSP and de-flux interactions, a study of OSP with four different de-flux cleaning chemistries is discussed. Various performance test methods are carefully examined to deliver a standard protocol for future OSP and de-flux interaction evaluations.
OSP coating thickness, appearance and solderability were evaluated as the OSP coating was processed through a typical substrate manufacturing process. Solder ball spread, and wetting balance tests were performed to evaluate the solderability. IMC evaluation, and solder joint integrity testing by ball shear, was performed to assess the effect of each cleaning chemistry on OSP soldering reliability.
Choosing a suitable OSP process and compatible cleaning chemistry can be a complex task with multiple variables at play, and not all processes are created equally! This paper aims to shed light on the significance of OSP coatings in safeguarding copper surfaces and improving solderability yield. It explains the interplay between coatings, cleaning agents, and other variables that dictate the effectiveness of OSP.
Collaborative testing with knowledgeable suppliers can aid in selecting the appropriate OSP coating, cleaning chemistry and assembly materials for optimal assembly yields.
Conclusions
The interaction between the OSP coating and the deflux cleaning process and chemistry is vitally important in IC substrate applications. It has been found that thicker OSP coatings will yield improved surface appearance after nitrogen reflow and deflux cleaning process steps. It has been shown that the interaction between the OSP coating and the various deflux process chemistries will yield differing amounts of coating thickness reduction. However, it is also shown that sufficient OSP coating will remain in place after the deflux cleaning processes that were tested. The solder ball spread, and ball shear performance test results provide assurance that excellent solderability is maintained, no matter which deflux cleaning chemistry is employed. The shelf-life test confirms the OSP maintains consistent performance over two years of shelf life.
Initially Published in the SMTA Proceedings
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