With the rapid development of high technology, electronic products closely related to the public are constantly updated, and the public also needs high performance, small size, and more functional electronic products, which puts forward new requirements for the circuit board. Double-sided circuit board is thus born, due to the wide application of double-sided circuit board, the printed circuit board manufacturing is also light, thin, short and small development.
1. circuit board welding skills
Circuit board welding tip 1:
The selective welding process includes: flux spraying, circuit board preheating, dip welding and drag welding. Flux coating process The flux coating process plays an important role in selective welding. At the end of welding heating and welding, the flux should be sufficiently active to prevent the generation of Bridges and prevent the oxidation of the circuit board. Flux spraying The board is carried by the X/Y manipulator over the flux nozzle, and the flux is sprayed onto the pcb board welding position.
Soldering circuit board Tips 2:
For microwave peak selective welding after reflow soldering process, it is important that the flux is accurately sprayed and the microporous spray type will not stain the area outside the solder joint. The spot diameter of the micro-spot spraying flux is greater than 2mm, so the position accuracy of the flux deposited on the circuit board is ±0.5mm, so as to ensure that the flux is always covered on the welding part.
Circuit board welding tip 3:
The process characteristics of selective welding can be understood by comparing with wave soldering. The obvious difference between the two is that the lower part of the circuit board in wave welding is completely immersed in the liquid solder, and in selective welding, some specific areas are in contact with the solder wave. Since the circuit board itself is a poor heat transfer medium, it will not heat and melt the solder joints in the area adjacent to the components and circuit board when welding.
The flux must also be pre-coated before welding, and compared with wave soldering, the flux is coated on the lower part of the board to be welded, rather than the entire pcb board. In addition, selective welding is applicable to the welding of plug-in components, selective welding is a new method, and a thorough understanding of the selective welding process and equipment is necessary for successful welding.
2. circuit board welding precautions
Remind everyone to get the PCB bare board should first carry out the appearance inspection, to see if there is a short circuit, open circuit and other problems, and then familiar with the development of the board schematic, schematic and PCB screen screen layer contrast, to avoid the schematic and PCB inconsistent.
After the materials required for PCB welding are ready, classify the components. All components can be divided into several categories according to their sizes for subsequent welding. A complete material list needs to be printed. In the welding process, if you have not finished welding one item, you will use a pen to cross out the corresponding options, so as to facilitate subsequent welding operations.
Before welding, take ESD measures, such as wearing ESD rings, to avoid electrostatic damage to components. After the welding equipment is ready, ensure that the soldering iron tip is clean and tidy. It is recommended to use a flat Angle soldering iron for initial welding, which can better contact the pad when welding such as 0603 package components. Of course, for the master, this is not a problem.
When selecting components for welding, welding should be carried out in accordance with the order of components from low to high and from small to large. In order to avoid the larger components welded to the smaller components welding inconvenience. Priority is given to welding integrated circuit chips.
Before welding integrated circuit chips, ensure that the chips are placed in the correct direction. For the chip screen printing layer, the general rectangular pad indicates the starting pin. When welding, a pin of the chip should be fixed first, and the diagonal pin of the chip should be fixed after fine-tuning the position of the components, so that the components are accurately connected to the position before welding.
There is no positive and negative electrode in the chip ceramic capacitor and voltage regulator circuit, and the positive and negative electrodes need to be distinguished in the light-emitting diode, tantalum capacitor and electrolytic capacitor. For capacitors and diode components, generally the clearly marked end should be negative. In the package of the patch LED, the direction along the lamp is positive-negative. For the silk-screen marked as diode circuit diagram package components, the vertical end should be placed on the diode negative extreme.
For the crystal oscillator, the passive crystal oscillator generally has only two pins, and no positive or negative points. Active crystal oscillator generally has four pins, and it is necessary to pay attention to the definition of each pin to avoid welding errors.
For the welding of plug-in components, such as components related to power modules, you can modify the device pins before welding. After the components are placed and fixed, the solder is generally melted on the back through the soldering iron and then integrated into the front by the pad. It is not necessary to put too much solder, but the components should be stable first.
PCB design problems found in the welding process should be recorded in time, such as installation interference, incorrect pad size design, component packaging errors, etc., for subsequent improvement. After the welding is completed, use a magnifying glass to check whether there is virtual welding and short circuit.
After the circuit board welding work is completed, alcohol and other cleaning agents should be used to clean the surface of the circuit board to prevent the iron filings attached to the surface of the circuit board to short-circuit the circuit, but also to make the circuit board more clean and beautiful.
3. double-sided circuit board characteristics
The difference between a single-sided circuit board and a double-sided circuit board is the number of layers of copper. Science popularization: Double-sided circuit board is a circuit board with copper on both sides, which can be connected through hole conduction. The single side has only one layer of copper, which can only be used for simple lines, and the holes made can only be used for plug-ins.
The technical requirements of the double-sided circuit board are that the wiring density is larger, the aperture is smaller, and the aperture of the metallized hole is smaller and smaller. Layer to layer interconnect depends on the metallization hole, quality is directly related to the reliability of the printed board.
With the reduction of the aperture, the original debris that has no effect on the larger aperture, such as brush debris and volcanic ash, once remaining in the small hole, will make the chemical precipitation of copper and copper plating lose their effect, and the hole is copper free, which becomes fatal to hole metallization.
4. Welding method of double-sided circuit board
In order to ensure that the double-sided circuit has a reliable conductive effect, it is recommended that the connection hole on the double panel (that is, the metallization process through the hole part) should be welded with a wire first, and the protruding part of the connection line should be cut to avoid stinging the operator's hand, which is the preparation for the connection of the board.
Two sided circuit board welding essentials:
The devices that require shaping shall be processed according to the requirements of the process drawings; That is, the model face of the diode after reshaping should face up, and the length of the two pins should not be inconsistent. When installing devices with polarity requirements, pay attention to the polarity should not be reversed, and the roller integrated block components, whether vertical or horizontal devices, should not be significantly tilted after installation.
The power of the soldering iron used for welding is between 25 and 40W, the temperature of the soldering iron head should be controlled at about 242 ° C, the temperature is too high, the head is easy to "die", the temperature is low, and the soldering time is controlled at 3 to 4 seconds.
Formal welding generally in accordance with the device from low to high, from the inside out of the welding principle to operate, welding time to master, too long time will burn the device, will also burn the copper covered plate on the copper covered wire strip. Because it is double-sided welding, a process frame for placing the circuit board should also be made, so as not to skew the device below.
After the circuit board is welded, it should be checked in many ways to check the place of missing insertion and welding, and trim the excess device pins on the circuit board after confirmation, and then flow into the next process. In the specific operation, the relevant process standards should also be strictly followed to ensure the welding quality of the product.
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