IWLPC (Wafer-Level Packaging) Conference Proceedings


VAPOR PHASE VS. CONVECTION REFLOW IN RoHS-COMPLIANT ASSEMBLY

Author: Chris Munroe
Company: EPIC Technologies
Date Published: 10/13/2008   Conference: IWLPC (Wafer-Level Packaging)


Abstract: The contract manufacturing industry is changing rapidly from lead-based soldering to lead-free soldering. There is no stopping the transition or the reality that lead-free components are going to be introduced in lead-based processes. This challenge to engineering and quality is a huge concern and one that needs scrutiny and a watchful eye. EMS providers rely on component suppliers to ensure that the lead-free transition on the component terminations is seamless to their soldering processes, but that rarely happens. Termination changes require additional modification to solder profiles and flux chemistries in order to ensure proper wetting of the solder to the lead-free termination. The need for nitrogen to be used in convection reflow is becoming a requirement more than an option, and nitrogen is costly.

Vapor phase (VP) reflow offers an advantage over convection in this lead-free transition phase. The inert environment and consistency of heat transfer allow VP to be more forgiving with lead-free component terminations. Less active no clean flux chemistries have proven to be adequate in soldering lead-free terminations that demand high activity fluxes in the convection reflow process.

An additional advantage of VP reflow is lower processing temperature. In convection or IR process temperatures can reach 245 to 265 degrees C at the component level. VP temperatures can be selected between 230 and 240 degrees C for lead-free processing. The lower temperatures make it possible to use standard FR substrate material rather than the higher cost FR406. Higher temperature substrate material can add 10-15% to PCB. VP also offers processing advantages with large mass connectors because the thermal equilibrium is better. In convection reflow, particularly in higher temperature lead-free processes, correctly soldering large mass connectors may overheat the rest of the PCBA.

This paper will look at the advantage and disadvantages of each technology in RoHS-compliant processing and discuss associated design for manufacturing (DFM) issues.



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