by
Jim Park
jdp4@st-andrews.ac.uk 01334 476161 ext 3144
NO RESPONSIBILITY IS ACCEPTED BY THE AUTHOR OR ANATEK CORP FOR THE INFORMATION IN THIS ARTICLE FOR ACCIDENTS, DAMAGE CAUSED WHETHER BODILY, MATERIAL OR FINANCIAL AS A RESULT OF THIS ARTICLE HOWEVER CAUSED. YOU HAVE BEEN WARNED. CHIP REMOVAL This procedure was developed for minimum cost as the described by Mark Neff in his very good article on How to DeSolder Surface Mount Components was too expensive. The equipment used was an electric hot air paint stripper, now this may sound like it will fry the board but it only takes seconds to loosen the chip from the pcb. The method is as follows: create an air dam round the component to be removed using copper strip . This prevents other components on the board getting too hot and migrating across the pcb. ** WARNING** pcb, tools & tweezers e.t.c. get very hot so be very careful not to burn yourself or others. It may be helpful to hold the hot air gun in a vice or retort stand ( as used by chemists )and hold the pcb in your hand with a welders glove on. The other hand will be used to move the Chip with tweezers. Turn the hot air gun on and position the pcb under the hot air stream over the chip to be removed for a few seconds try to move the Chip with the tweezers DO NOT FORCE. Once the Chip is hot enough it can be either shifted to one side or lifted clear with the tweezers with no damage to the pads and tracks on the pcb. Another method is to secure the pcb in a vice and hold the air gun and tweezers in either hand whichever is the most comfortable. Whatever method is used be careful things can get very hot!. CHIP SOLDERING **WARNING** soldering irons are very hot treat with care. I have also soldered surface mount chips with a normal electronic size soldering iron using a fine tip. The method I use is to position the chip using tweezers and soldering iron to anchor the chip on two diagonally opposite pins to the two pre-tinned pads on the pcb, it does not matter if pins are shorted togther as this will be fixed later. Now comes the barbaric procedure using the soldering iron solder all the pins together by applying the soldering iron and solder while moving along the sides of the chip and pads. Do this procedure quickly but be sure the solder is wetting properly. Once all the pins of the chip are shorted together with solder use desolder wick to remove the excess solder until all the shorts are gone. Thats all there is to it and if you have none of the expensive rework equipment then it may be the only way to do the job. The methods described above sound barbaric but have been used to manually build and rework 100s of pcbs in a minimum cost production environment.
Article by Jim Park University of St Andrews, Dept Physics & Astronomy, North Haugh, St Andrews, Fife, Scotland UK 01334 476161 ext 3144.
