Removal of High Density Plated Through Hole Connectors on Large Mass Multi-Layered Circuit Card AssembliesAuthor: Michael Newman
Company: Harris Corporation
Date Published: 9/28/2014 Conference: SMTA International
Assembling these complex backplane CCAs is a task in itself that can only be done using automated Selective Solder Reflow Equipment. This equipment has the capability to pre-heat the CCA and keep it at a temperature that when the solder fountain does its work the amount of heat loss is minimized ensuring a through solder joint between the connector pins and PWB PTHs. What happens when a connector is defective or becomes damaged during assembly or any other reason that requires this connector to be replaced?
Traditional methods of using soldering iron and solder wick just don't work due to the thickness of the PWB and the typically large power and ground planes (2 – 3oz copper layers). Solder fountains might work if the PWB finish was Electroless Nickel Immersion Gold (ENIG) or maybe even Electroless Nickel / Electroless Palladium Immersion Gold (ENEPIG) but because of the HASL finish and the amount of time over the wave required to reflow the entire joint there is a real danger of dissolving the copper annular rings as well as the PTH barrels.
This paper will discuss the use of Hot Air rework equipment to effectively remove the solder and connector from these large mass high density backplanes without damaging adjacent connectors or any of the PWB metallization. Topics of discussion will include equipment selection, some general process parameters as well as some validation criteria and lessons learned.
Rework, Backplane, PTH, HASL, Intermetallic
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