Due to the high melting point temperature, poor wettability and small process window of the prototype pcb lead-free alloy. The PCB pad is most damaged during manual soldering and rework
, because the commonly used FR-4 epoxy glass fiber copper clad laminate is bonded to the glass fiber cloth by adhesive glue under high temperature and high pressure. Can withstand 290 ° C high temperature. It can be seen from Fig. 1 that there is a process window of 60 °C between the peak temperature of Sn-Pb soldering and the limit temperature of PCB brazing, and the process of lead-free (Sn-3.8Ag-0.7Cu) soldering with only 30 °C process window.
Since the manual soldering is exposed to the air, the heat dissipation is fast, and the temperature of the lead-free soldering iron tip is generally between 360 and 410 ° C. In the case where the thick plate of the prototype pcb, the large heat capacity component, the large pad, the thick lead, etc. are difficult to weld, It may need up to 420 °or above C, so it is easy to make the pads fall off.
(1) Precautions for lead-free manual soldering and rework.
● Choose the suitable welding and rework equipment and tools.
● Using of welding and rework equipment and tools correctly.
● Choose the solder paste, flux, solder wire and other materials correctly.
● Set the welding parameters (temperature curve) correctly.
● Pay attention to the number of potential electrostatic discharge (ESD) hazards.
● When removing the device, remove the device when all the pins are completely melted to prevent damage to the components and the pads from falling off. Should take care during the repair process to minimize any potential factors that adversely affect the reliability of components and PCBs.
(2) Pay attention to the lead-free manual soldering temperature and time.
(3) Main measures corresponding to lead-free manual welding.
● Master the correct welding method.
● Increase flux activity.
● Increase the welding temperature.
● Properly extend the welding time.
● Clean the residue in time.
The above are hand soldering techniques and rework technology. hoping it is helpful to you!