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I. Related information
1. How to deal with the Voids produced by the lead BGA in lead-free soldering?
As the development of the lead-free technology, more and more SMT processing enterprises
come across the problem of Voids in production.
Many companies try to avoid using lead BGA in lead-free soldering technology. Because the
melting point of lead soldering balls is lower than lead-free tin paste. The tin balls melt first and
surround the tin paste, so that the flux in the paste can't volatilize, and form bubbles inside. If there
is via on the soldering pad, there may be more bubbles.
Steps of desoldering and replacing BGA/CSP with lead-free desoldering materials:
Set the temperature curve;
Desoldering the broken parts;
Clean and preparation for the repair work;
Remount the reworked parts with flux paste.
Detection of reflow soldering.
a. Requirement of devices in reworking
Repairing method of BGA/CSP is convection, not radiation, so soldering iron is not the ideal
choice. In normal reworking of BGA, it is difficult to use IR, because the ceramic heater can't cool
down very quickly, thus it is difficult to control the time of higher reflow temperature. However, the
convection can control strictly, and it is conductive to a better & repeatable temperature curve, and
the components will not be over-heated, and the time of higher reflow temperature will not prolong
too much.
The standard reflow consists of 3 temperature areas: preheating area, insulation area and
reflow area. After reflow, it is the process that PCB cools down to less than 100 . The soldering
process is more important in lead-free assembly. Lead-free process calls for temperature as high as
235 , but BGA/CSP is sensitive to high temperature. Then the wrong temperature rising will bur
℃
the components.
Semi-auto reflow retrieval system can save many temperature curves. It is important to know
the use of temperature curves. A precise temperature is the key point in the production which can
ensure that all the welding points heat and reach the peak temperature together. The starting point
of the production parameter is the actual temperature of PCB. The technician can adjust the heating
area parameter of the machine to achieve the expected temperature curve of PCB through the
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