PCBA Tech - smt disassembly and raw material quality inspection

Disassembly skills of smt patch components

Generally speaking, it is not so easy to remove smt patch components. Constant practice is required to master it. Otherwise, it is easy to damage smd components if they are forcibly disassembled. The mastery of these skills of course requires practice

Generally speaking, it is not so easy to remove the components of smt patch processing. Constant practice is required to master it. Otherwise, it is easy to damage smd components if they are forcibly disassembled. Of course, the mastery of these skills requires practice. It is roughly divided into three situations to describe.

1. For components with few smd components, such as resistors, capacitors, diodes, transistors, etc., first plate tin on one of the pads on the PCB board, and then use tweezers to hold the component to the mounting position and hold it against the circuit board with your left hand. Use a soldering iron to solder the pins on the tin-plated pad with your right hand. The left-hand tweezers can be loosened, and solder the remaining feet with tin wire instead. If you want to disassemble this kind of component, it is easy, just use a soldering iron to heat both ends of the component at the same time, and then gently lift the component after the tin is melted.

2. For components with more pins for smt chip processing, and chip components with wider spacing, a similar method is used. First, tin plate on one pad, and then use tweezers to clamp the component with the left hand to solder one foot OK, then use tin wire to solder the remaining feet. The disassembly of this type of component is generally better with a hot air gun. One hand holds the hot air gun to blow the solder, and the other hand uses tweezers and other fixtures to remove the component while the solder is melting.

3. For components with higher pin density, the soldering steps are similar, that is, solder one pin first, and then solder the remaining pins with tin wire. The number of pins is relatively large and dense, and the alignment of the pins and the pads is the key. Usually choose the soldering pads on the corners with only a little tin plated. Use tweezers or hands to align the components with the soldering pads, align the edges with pins, press the components on the PCB with a little force, and solder them with a soldering iron. The corresponding pins of the disk are soldered well. Do not shake the circuit board vigorously, but gently rotate it, and solder the pins on the remaining corners first. After the four corners are soldered, the component will basically not move, solder the remaining pins one by one. When soldering, apply some pine perfume first, with a small amount of tin on the head of the soldering iron, and solder one pin at a time.

Finally, it is recommended that the disassembly of high-pin-density components mainly use a hot air gun, clamp the components with tweezers, blow all the pins back and forth with the hot air gun, and lift the components when they are all melted. If there are more components to be removed, try not to face the center of the components when blowing, and the time should be as short as possible. After the components are removed, use a soldering iron to clean the PCB pads.

Tasks and methods of SMT raw material quality inspection

The task of raw material quality inspection includes four aspects: raw material quality judgment, quality problem prevention, quality information feedback and quality problem arbitration. Quality judgment refers to judging the qualification or quality level of raw materials through testing in accordance with relevant quality requirements and specifications. Quality problem prevention refers to the use of quality inspections to ensure that unqualified raw materials are not put into use, so as to prevent the resulting quality problems. Quality information feedback refers to the feedback of quality problems existing in raw materials to relevant departments or cooperating enterprises through quality inspection, to find out the causes of quality problems in time, and to provide a basis for improving quality. Quality issue arbitration refers to the use of scientific quality inspection and evaluation methods to determine the cause and responsibility of quality issues when raw material suppliers and recipients have objections or disputes over quality issues.

The methods of SMT raw material quality inspection include sensory inspection, appliance inspection, and trial inspection. Sensory testing refers to testing that uses human sensory organs as a testing tool to evaluate the quality of raw materials. It is mainly used for qualitative testing of the product's appearance, color, scars, smell, and other intuitive and external content. Instrument testing refers to the use of instruments, measuring tools, testing equipment and other testing tools to detect product quality characteristics using physical or chemical methods, for example, the physical and chemical characteristics of SMT raw materials such as performance, strength, hardness, and reliability. Trial testing refers to the identification of the quality or characteristics of raw materials through actual use. This testing method is mostly used to identify the quality of new materials.