VAPOR PHASE VS. CONVECTION REFLOW IN RoHS-COMPLIANT ASSEMBLYAuthor: Chris Munroe
Company: EPIC Technologies
Date Published: 10/13/2008 Conference: IWLPC (Wafer-Level Packaging)
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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