With the development of market economy and the growth of all aspects of life, you may not know very much about PCBA processing. Today, I' ll talk about the topic of PCBA processing. Do you know what are the methods of PCBA processing? What are the common problems? Next, we will give a detailed introduction of "PCBA processing desoldering skills and daily problems".
【Introduction of desoldering skills in PCBA processing】
1. Basic principles of ：
Be sure to understand the characteristics of the original solder joints before desoldering. Do not use it easily.
(1) Do not damage the components, wires and surrounding components to be removed;
(2) Do not damage the pads and printed conductors on the pcb during desoldering;
(3) For the electronic components that have been judged to be damaged, the pins can be cut and then removed, which can reduce the damage;
(4) Try to avoid moving the position of other original devices, and if necessary, you must do a good job of recovery.
2. Working points of desoldering:
(1) Strictly control the temperature and time of heating to avoid damage to other components at high temperatures. The time and temperature of general desoldering are longer than when welding.
(2) Do not use excessive force during desoldering. The package strength of components at high temperatures is degraded, and excessive pulling, twisting and twisting can damage components and pads.
(3) Aspirate the solder on the solder joint. The solder can be sucked by the soldering tool to directly remove the components, reducing the time for soldering and the possibility of damage to the pcb。
3. Desoldering method:
(1) Split point welding method
For the horizontally mounted resistance-capacitor components, the distance between the two solder joints is far, and the soldering iron can be heated by points and pulled out point by point. If the pin is bent, use a soldering iron to straighten it and then remove it.
When desoldering, erect the pcb and use a soldering iron to heat the solder joints of the components to be removed. Gently pull out the component pins with tweezers or needle-nosed pliers.
(2) Centralized desoldering method
Since the pins of the row resistor are separately soldered, it is difficult to heat them at the same time by using an electric soldering iron. A hot air welder can be used to rapidly heat several solder joints, and the solder is melted and then pulled out once.
(3) Retaining the welding method
Use the suction tool to pick up the solder of the removed solder joint. In general, components can be removed.
In the case of multi-pin electronic components, it can be heated by means of an electronic hot air blower.
If it is a lapped component or pin, you can apply flux to the solder joint, solder the solder joint, and remove the component leads or wires.
If it is a hook-welded component or pin, first remove the solder of the solder joint with a soldering iron, then heat it with a soldering iron to melt the residual solder under the hook, and lift the pin with a blade in the direction of the hook. Do not use too much force to prevent splashing of molten solder into your eyes or clothing.
(4) Shearing and desoldering method
If there are any spare parts or wires on the solder joints, or if the components are damaged, you can cut off the components or wires and then remove the wire ends on the pads.
4. Problems to be aware of when re-welding after desoldering
(1) The components and wires of the re-welded components should be as consistent as possible;
(2) punching through the blocked pad hole;
(3) Restore the moved components to their original state.
【Common Problems and Solutions in PCBA Processing】
Poor wetting
Phenomenon: During the soldering process, the substrate soldering area and the solder do not react with each other after infiltration, resulting in less soldering or soldering.
Cause Analysis:
(1) The surface of the pad is contaminated, the surface of the pad is stained with flux, or the surface of the chip component is a metal compound. Will cause poor wetting. For example, sulfides on the surface of silver, oxides on the surface of tin, etc., may cause poor wetting.
(2) When the residual metal in the solder exceeds 0.005%, the degree of flux activity is lowered, and poor wetting occurs.
(3) When wave soldering occurs, gas is present on the surface of the substrate, and it is easy to cause poor wetting.
solution:
(1) Strictly implement the corresponding welding process;
(2) The surface of the pcb board and components should be cleaned;
(3) Select the appropriate solder and set a reasonable soldering temperature and time.
2. Monument
Phenomenon: One end of the component does not touch the pad and is inclined upward or the contact pad is upright.
Cause Analysis:
(1) The temperature rises too fast during reflow soldering, and the heating direction is not balanced;
(2) Select the wrong solder paste, no preheating before soldering and incorrect selection of solder joint size;
(3) The shape of the electronic component itself is easy to produce a monument;
(4) It is related to the wettability of solder paste.
solution:
1. Store and access electronic components as required;
2. Reasonably establish the temperature rise of the reflow zone;
3. Reduce the surface tension generated on the end of the component when the solder melts;
4. Reasonably set the printing thickness of the solder;
5. Pcb needs to be preheated to ensure uniform heating during welding.