PCB Assembly skills 1
The process of selective soldering includes: flux coating, board preheating, dip soldering and drag soldering. Flux Coating Process In the selective soldering process, the flux coating process plays an important role. At the end of solder heating and soldering, the flux should be sufficiently active to prevent bridging and prevent oxidation of the board. The flux is sprayed by the X/Y robot carrying the board through the flux nozzle and the flux is sprayed onto the pcb board soldering position.
Prototype PCB assembly skills 2
The microwave peak after the reflow soldering process, the most important thing is that the flux is accurately sprayed, and the micropore jet type will never contaminate the area outside the solder joint. The minimum solder dot pattern diameter of micro-spraying is greater than 2mm, so the solder placement accuracy of the solder deposited on the board is ±0.5mm to ensure that the flux always covers the soldered portion.
The characteristics of selective soldering can be understood by comparison with wave soldering. The most obvious difference between the two is that the lower part of the board in the wave soldering is completely immersed in the liquid solder. In the selective soldering, only some specific areas are Solder wave contact. Since the board itself is a poor heat transfer medium, it does not heat the solder joints that melt adjacent components and board areas during soldering.
Flux must also be pre-coated prior to soldering. Flux is applied only to the portion of the board to be soldered, rather than the entire PCB board, compared to wave soldering. In addition, selective soldering is only suitable for the soldering of the interposing components. Selective soldering is a completely new way to thoroughly understand that selective soldering processes and equipment are necessary for successful soldering.
PCB Board soldering precautions
1. After getting the bare PCB, first check the appearance to see if there is any short circuit or open circuit. Then familiarize yourself with the schematic diagram of the development board and compare the schematic with the PCB screen to avoid the schematic and the PCB.
2. After the materials required for PCB welding are ready, the components should be classified. All components can be divided into several categories according to the size, which is convenient for subsequent welding. Need to print a complete bill of materials. In the welding process, if one item is not welded, the corresponding option is crossed out with a pen, which is convenient for subsequent welding operations.
Wear antistatic measures such as static rings before soldering to prevent static electricity from harming components. After the equipment required for welding is ready, the tip should be clean and tidy. For the first time welding, it is recommended to use a flat angle soldering iron. When soldering components such as 0603, the soldering iron can better contact the pad for soldering. Of course, for the master, this is not a problem.
3. When selecting electronic components for soldering, soldering should be performed in the order of components from low to high and from small to large. In order to avoid welding large components, the welding of smaller components is inconvenient. Prior to soldering integrated circuit chips.
4. Before the soldering of the integrated circuit chip, it is necessary to ensure the correct orientation of the chip. For a chip silkscreen, a generally rectangular pad represents the starting pin. When soldering, fix one pin of the chip first, fine-tune the position of the component, and fix the diagonal pin of the chip so that the component is accurately connected and soldered.
5. SMD ceramic capacitors and voltage regulator circuits have no positive and negative poles. The LEDs, tantalum capacitors and electrolytic capacitors need to distinguish between positive and negative electrodes. For capacitors and diode components, the one that is generally marked should be negative. In the package of the chip LED, the direction along the lamp is in the positive-negative direction. For the silk screen identification component of the diode circuit diagram package, the negative terminal of the diode should be placed at one end of the vertical line.
- 6. For the crystal oscillator, the passive crystal oscillator generally has only two pins, and there is no positive or negative. The active crystal oscillator generally has four pins, so pay attention to each pin definition to avoid soldering errors.
- 7. For the soldering of plug-in components, such as power module related components, the device pins can be modified before soldering. After the components are placed and fixed, the solder is usually melted on the back side by a soldering iron and then integrated into the front surface by the pads. Solder does not have to be placed too much, but the components should first be stabilized.
- 8. The PCB design problems found in the soldering process should be recorded in time, such as installation interference, incorrect pad size design, component package errors, etc., for subsequent improvement.
- 9. After welding, use a magnifying glass to check the solder joints to check if there are any solder joints and short circuits.
- 10. After the welding work of the circuit board is completed, the surface of the circuit board should be cleaned with a cleaning agent such as alcohol to prevent the iron scraps attached to the surface of the circuit board from short-circuiting the circuit, and at the same time, the circuit board can be made more clean and beautiful.
2-Lalyer board features
The difference between a single-sided board and a double-sided pcb board is that the number of layers of copper is different. The double-sided circuit board has copper on both sides of the circuit board, which can be connected through the via hole to connect. There is only one layer of copper on one side, and only a simple circuit can be used. The holes made can only be used for plug-ins that cannot be turned on. The technical requirements of the double-sided circuit board are that the wiring density is increased, the aperture is smaller, and the metallized hole aperture is also smaller. The quality of the metallized holes on which the layers are interconnected depends on the reliability of the printed board. As the pore size shrinks, the original impurities that have no effect on the larger pore size, such as grinding debris and volcanic ash, will remain in the small holes, which will cause the chemical copper and copper plating to lose their effect, and the holes will be free of copper and become holes. Metalized deadly killer.
2-layer board assembly method
In order to ensure the reliable electrical conduction effect of the double-sided circuit board, the connection hole (ie, the metallization process through-hole part) of the double-sided board should be first welded with a wire or the like, and the protruding portion of the connection line tip should be cut off to avoid 剌 Injury the operator's hand, this is the board's wiring preparation work.
Double-sided board soldering essentials:
1.For devices that require shaping, the process should be processed according to the requirements of the process drawings; that is, the plug-in is shaped first.
2.After the shaping, the model surface of the diode should face upwards, and there should be no inconsistency between the lengths of the two pins.
3. When inserting the device with polarity requirements, it should be noted that the polarity should not be reversed. The roller is integrated with the block components. After the instrument is inserted, no vertical tilt or flat device can be tilted.
4. The electric soldering iron used for soldering has a power of 25~40W. The temperature of the soldering iron tip should be controlled at about 242°C. The temperature is too high and the head is easy to “die”. The temperature is low and the solder can not be melted. The welding time is controlled at 3. ~4 seconds.
5. the formal welding is generally in accordance with the device from short to high, from the inside to the outside of the welding principle to operate, welding time should be mastered, too long will burn the device, it will burn the copper line on the copper plate.
6. Because it is double-sided soldering, it should also be used as a process frame for placing circuit boards, etc., in order not to tilt the device below
7. After the welding of the circuit board is completed, a full check-in type inspection should be carried out to check the place where the leakage welding is performed. After confirming, the excess device pins of the circuit board are trimmed, and then flow into the next process.
8. In the specific operation, it should also strictly follow the relevant process standards to ensure the welding quality of the products.
With the rapid development of high technology, electronic products closely related to the public are constantly being updated, and the public also needs electronic products with high performance, small size and many functions, which puts new requirements on the circuit board. The double-sided circuit board was born because of the wide application of the double-sided circuit board, which has led to the development of printed circuit board, which is light, thin, short and small.