At present, many companies are using lead-free solder paste
products and processes, so lead-free environmental protection solder paste is an important part of the lead-free process, and its performance is attracting more and more attention. The following is based on the product development of lead-free ring solder paste, and discusses in depth some problems caused by lead-free processing technology, such as alloy selection, printability, ultra-low temperature reflow, void level, etc. At the same time, today’s Jiajinyuan editor Introduced to you the corresponding characteristics of the new generation of lead-free solder paste products.
Lead Free Solder Paste
Because the relative density of Sn/Ag/Cu alloy (7.5g/mm3) is lower than that of Sn-Pb alloy (8.5g/mm3), the printing performance of lead-free solder paste using this alloy is worse than that of lead-based solder paste Some, such as very easy to stick scraper and so on. Even so, because ensuring better printability of solder paste is critical to improving SMT productivity and controlling costs, in the case of the same alloy composition, the only way to improve the printability of solder paste is to adjust the solder paste composition, such as Filling mesh capacity, wet strength, anti-cold / hot collapse and wet environment ability, etc., and thus increase the printing speed and improve the printing effect.
2. Necessity of return
Because the melting point of lead-free alloys increases (the melting point of Sn/Ag/Cu alloy is 217°C, and the melting point of Sn-Pb alloy is 183°C), the main problem encountered by lead-free processing technology is the highest value in the reflow oven. increase in temperature. When the lead-free environment protection solder paste flows back to the electric soldering, under the worst case assumption (the PCB circuit board is the most complicated, the system deviation and data error are positive, and it reaches the standard of sufficient infiltration), the hottest spot on the PCB circuit board The temperature is very likely to be achieved (265°C).
3. Alloy selection
In order to find a suitable lead-free alloy to replace the traditional Sn-Pb alloy, we have done a lot of attempts. This is because there are many factors to be considered in the selection of lead-free alloys, such as melting point, impact toughness, shelf life, cost and so on.
4. Hollow level
Void is a commonly used defect in reflow soldering, especially on electronic devices such as BGA/CSP. Due to the large differences in the size, location, proportion and measurement range of the void, the safety assessment of the void level has not been unified so far.