Authored By:
Adzahar Samat and KL Chia
Venture Corporation Limited.
Singapore
Transcript
Vapor Phase soldering is a method of reflow technology developed by ATT Labs back in the 80s. Then, Vapor Phase soldering was the preferred reflow soldering technology because of its excellent heat transfer capability.Heat transfer to the PCB is accomplished almost irrespective of the shape and thermal mass involved.The physically defined and unchangeable heat transfer of the condensing vapor ensures consistent repeatability and reproducibility.There were associated disadvantages using vapor phase such as fast temperature rise, limited influence on the temperature profiles and high costs.As such the use of Vapor Phase Soldering was reduced to special applications with high mass or complex boards in low volume. Over the last few years, a new Vapor Phase procedure and new machines were developed.This paper will investigate the latest Vapor Phase soldering technology and compare its performance with convection reflow soldering technology. The results from the evaluation on solder joint quality and joint strength, will be described in detail.
Summary
Vapor Phase soldering is a method of reflow technology developed by ATT Labs in NJ back in the 80s. Then, Vapor Phase soldering was the preferred reflow soldering technology because of its excellent heat transfer capability. Heat transfer to the pcb is accomplished almost irrespective of the shape and thermal mass involved. The physically defined and unchangeable heat transfer of the condensing vapor ensures consistent repeatability and reproducibility.
There were associated disadvantages like fast temperature rise, nearly no influence on the temperature profiles and high costs. As such the use of Vapor Phase Soldering was reduced to special applications with high mass or complex boards in low volume (e.g. for military or aerospace application). Over the last few years, a new Vapor Phase procedure and new machines were developed. Vapor Phase Soldering now offers new features for soldering, especially helpful when changing to Pb-free soldering. The main
advantages of a state of the art Vapor Phase system are low process temperatures, freely adjustable temperature gradients and profiles, automatically controlled time above liquidus (TAL) and a perfect automatic inert gas atmosphere.
This paper will investigate the latest Vapor Phase soldering technology and compare its performance with convection reflow soldering technology. It will include a comprehensive process development with No-Clean Pb-free assembly carried out in Venture Corporation, Limited. The results were verified by employing different techniques, 5DX, SIR, Pull Test and Shear Test, micro-cross sectioning and SEM analysis. Effects of solder paste formulation, reflow profiles, time above liquidus and stencil aperture design on voids in vapor environment were determined.
Minimum delta T repeatability and maximum vapor reflow cycles to delamination was characterized. Results from the evaluation on solder joint quality and joint strength, will be described in detail.
Conclusions
Vapor Phase soldering qualification was run using optimized parameters. The data from solder joint quality of voids, intermetallic thickness and older joint strength verified through pull and shear test indicates Pb-free solder paste A produced the best solder joint quality and strength in Vapor Phase soldering environment.
Time-above-liquidus (TAL) and reflow profile have large effects. 1.02C/sec(Ramp), 30 sec (TAL), produced smaller voids. Vapor Phase soldering process produces excellent wetting and shinier solder joints as compared to convection reflow process. Vapor Phase soldering allows high thermal mass components to be reflowed with small delta T between adjacent smaller components. The pcb can withstand more than 10 Vapor Phase reflow cycles without delamination.
Initially Published in the SMTA Proceedings
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