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What is False Soldering? What is false soldering?
1.False soldering means that the component pins, soldering ends, PCB pads are not sufficiently tinned, the wetting angle of the solder in this place is greater than 90 °, and only a small amount of solder to wet the pins, soldering ends, PCB pads, resulting in poor contact with the time on and off. Virtual soldering is generally oxidation or impurities in the soldering point and the soldering temperature is not good, improper method caused by the essence of the solder and the pins of the existence of isolation between the layer. They are not completely in contact with each other. The naked eye generally can not see its state. However, its electrical characteristics do not conduct or poor conductivity, affecting the circuit characteristics. False soldering welded but not completely welded, easy to fall off.
2.False soldering refers to the component pins, the solder end on the tin is good, from the surface has formed a good solder joints, but the solder joints inside the solder and PCB pads between the formation of a good weld, when the solder joints are subjected to external forces can be easily detached from the pads. False soldering means that the surface seems to be soldered, but in fact not soldered. Sometimes the lead wires can be pulled out of the solder joints by hand. False soldering on the surface seems to be welded, but in fact not welded at all, a touch will fall off, more likely to fall off than false soldering.
3.Empty soldering is a solder joint that should be soldered but is not. Too little solder paste, the problem of the parts themselves, the position of the parts, too long a period of time after the printing of tin...etc. will cause empty soldering.
4.Cold soldering is the failure to form a soldering band at the soldering interface of the part (i.e. poor soldering). Cold soldering can be caused by too low soldering temperature, too short soldering time, and soldering problem.
Hazards of false soldering
False soldering is mainly caused by the oxides and dirt on the surface of the metal to be soldered, its solder joints into a contact resistance connection state, resulting in the circuit does not work properly, the appearance of the unstable phenomenon of the good times and bad times, the noise is added without regularity, to the debugging of circuits, the use of maintenance and maintenance of a major hidden danger. In addition, there are part of the false soldering in the circuit began to work for a longer period of time, keep in touch with the good, this is not easy to find. But in the temperature, humidity and vibration and other environmental conditions to push the election, the contact surface is gradually oxidised,the contact slowly become incomplete up.
The contact resistance of the virtual soldering false point will cause local heating, local temperature rise and promote incomplete contact of the solder joints further deterioration of the situation, and ultimately even make the solder joints fall off,the circuit can not work properly. This process can sometimes take up to one or two years. According to statistics show that in the electronic machine product failures, nearly half is caused by poor welding, however, to find out from a thousands of soldering points in the electronic equipment caused by the failure of the virtual soldering point to, it is not an easy thing.
Therefore,soldering is a major risk to circuit reliability and must be strictly avoided. Particular attention should be paid to manual soldering operations. The existence of false soldering greatly reduces the circuit board printing and the overall reliability of the product, to the production process resulting in unnecessary maintenance, new production costs, reduce production efficiency, to the products already out of the factory caused by a great deal of quality, safety hazards, new after-sales maintenance costs.
Detection methods of false welding
1.Visual inspection method
General first look for heating components, such as power tubes, high-current diodes, high-power resistors, integrated circuits, etc., these components because of the heat prone to virtual welding, serious direct can be seen, minor can be viewed with a magnifying glass. Generally just welded pins are very smooth. When the edge is affected, due to constant extrusion and stretching, will become rough and glossy, around the solder joints will appear grey circle, with high magnification can be seen in the tortoise crack-like small cracks group, the seriousness of the formation of ring-shaped cracks, that is, desoldering. Therefore, even if there is no desoldering in the place of the ring-shaped black circle, it is a hidden danger in the future. Large area patch welding integrated circuits, heating element pins is one of the solutions.
2.Current detection method
Check whether the current setting is in line with the process requirements, there is no change in the product load current setting is not correspondingly added, so that the welding current is insufficient to produce welding defects.
3.Shaking method
Is to use a hand or camera to the low-voltage components one by one to shake, in order to feel the components have no loosening phenomenon, which should be mainly on the relatively large components to shake. In addition, before using this method, the fault area should be compressed. Determine the approximate scope of the fault, otherwise facing a large number of components. Shaking one by one is very unrealistic.
4.Vibration method
When encountered when the phenomenon of virtual welding, you can take the method of knocking to confirm,with a screwdriver hand Bing gently tapping the circuit board to determine the location of the virtual welding point. But in the use of percussion method, should ensure personal safety, but also to ensure the safety of the equipment,so as not to expand the scope of the failure.
5.Soldering method
Patch welding method is when a careful inspection still can not be found after the failure of a maintenance method,that is,the scope of the failure of the components one by one for welding. In this way, although the real fault is not found, but can achieve the purpose of maintenance.
What are the reasons for false soldering?
1.Defects in the design of the soldering pads and the presence of through holes in the pads.
2.The position of the solder joints is polluted by oxides and other impurities, making it difficult to apply solder.
3.The PCB board is damp.
4.Improper flux selection, or poor activity, or has been invalid, resulting in poor wetting of the solder joints.
5.Component soldering ends, pins, oxidation, resulting in poor solderability.
6.Components, pad heat capacity, component pins, pads do not reach the soldering temperature.
7.Printed solder paste is affected by scratching and rubbing in the process of opening and printing, resulting in a decrease in the amount of solder paste.
How to prevent causing false soldering?
1.Defective design of pads. There should not be any through holes in the pads, as these holes will cause loss of solder and result in insufficient solder. Pad spacing, area also need to match the standard, otherwise the design should be corrected as soon as possible.
2.PCB board has oxidation phenomenon, that is, the pad is not bright. If the oxidation phenomenon, the rubber can be used to remove the oxide layer, improve the tin effect.
3.PCB board moisture, PCB in the dry box 110 ° baking 8H.
4.Select a good active solder paste, the paste should be used up within 24H after opening the lid.
5.Materials should be stored and transported reasonably according to the requirement of humidity sensitivity to avoid moisture and oxidation of materials.
6.According to the product device, PCB layout, material set a reasonable furnace temperature curve.
7.Set up the parameters of the printing machine, according to the standard work, to ensure that the production of the printing effect is OK.
False soldering false soldering is a common occurrence in the PCBA processing bad phenomenon, the above is the PCB and PCBA manufacturer to share with you what is false soldering, false soldering? What are the causes of false soldering? How to prevent false soldering?