Ask the Experts
August 31, 2009
Small Chip Cap Rework Advise
What are the best tools and techniques you suggest for rework of small components such as 0201 and 0402 chip caps on circuit board assemblies?
Also would the tools or techniques change when the circuit board assemblies have heavy ground planes?
Do you lean toward conduction tools or convection tools when reworking such small components?
Expert Panel Responses
Without a doubt, there are two main issues regarding small passive component rework.
First, can you see them? Not just a blurred outline - but a clear, non resolution-limited image.
Second, when the cap is removed, is it the only thing removed?
It's relatively easy to heat, pick and dispose of a bad device, ask anyone skilled with tweezers and a fine tipped soldering iron. But down in the 0402/0201/01005 domain - it's not so easy!
So, a thermode nozzle that combines convection and conduction is the ideal tip in a high quality rework system. Temperature controlled hot-gas (preferably N2) streams through the nozzle body transferring heat via conductive contact between the tip and the cap.
The effectiveness of the process can be judged by how close neighboring components are undisturbed during reflow and replacement. Due to their small thermal mass, whether the board has heavy ground planes should not be an issue, as the process is top-side dominated.
Neil O'Brien has worked in the field of electronic manufacturing equipment for over fifteen years and is currently Sales Director for Finetech, a manufacturer of precision rework systems and die bonders.
Reworking sub-mm components requires either highly skilled operators with very reliable hand held equipment and vision assist or accurate semi-automated rework systems. Lead-free alloys do not self-align components nearly as well as lead based, resulting for the need of increased precision.
In both cases, necessary controls are required to ensure repeatable rework. Rework systems minimize operator dependencies and operator to operator inconsistencies. When challenged with rework applications with heavy ground planes, pre-heating assemblies improves overall heat transfer.
Both conduction and convection deliver more than adequate heat transfer, provided they are implemented correctly.
Regional Sales Manager
Al Cabral is Regional Sales Manager for Finetech and Martin rework products. His expertise includes through-hole, surface mount and semiconductor packaging with an emphasis on soldering and heat transfer. Al has been a significant contributor to the development and optimization of reflow and rework processes and systems, particularly lead-free transitions and microelectronic applications.
The fastest method would involve a bottom side convection pre-heater, a board holder, and a direct power soldering system equipped with precision conductive tweezers handpiece.
Fixture the PCB into the board holder and position it over the pre-heater, after the board is warmed to 100C, power on the direct power soldering system, now using the tweezers simply grasp the components with the tweezers and lift off after reflow.
This method will work on high mass boards and it also works very well under a microscope.
Regional Sales Manager
OK International Inc.
Mr. Zamborsky serves as one of OK's technology advisers to the Product Development group. Ed has authored articles and papers on topics such as; Low Volume SMT Assembly, Solder Fume Extraction, SMT Rework, BGA Rework, Lead Free Hand Soldering, Lead Free Visual Inspection and Lead Free Array Rework.