Wave soldering machine is now a necessary equipment in the welding of electronic products plug-in, but wave soldering often encounter wave soldering bad problems due to various reasons, to solve the problem must know the causes of wave soldering defects.
I. A wave solder is not enough: solder joints dry / incomplete / hollow, plug-in holes and guide holes solder is not full, solder is not climbing to the component surface of the pad.
Causes.
a) PCB preheating and soldering temperature is too high, so that the viscosity of the solder is too low.
b) Cartridge hole aperture is too large, solder from the hole out.
c) Inserted components fine lead large pads, solder is pulled to the pad, so that the solder joint dried out.
d) Poor quality metallization holes or solder resist flowing into the holes.
e) PCB climbing angle is small, which is not conducive to the exhaust of solder.
Solution countermeasures.
a) Preheating temperature of 90-130 ℃, more components to take the upper limit, the tin wave temperature of 250 + / -5 ℃, welding time 3 ~ 5S.
b) Cartridge hole diameter than the pin diameter 0.15 ~ 0.4mm, fine lead to take the lower limit, thick lead to take the upper line.
c) Solder pad size and pin diameter should match, to facilitate the formation of the curved moon surface.
d) Reflected to the PCB processing plant to improve the quality of processing.
e) PCB climbing angle of 3 to 7 ℃.
II. Wave solder too much: component solder ends and pins are surrounded by too much solder, the wetting angle is greater than 90 °.
Causes.
a) The soldering temperature is too low or the conveyor belt speed is too fast, making the viscosity of the molten solder too large.
b) PCB preheating temperature is too low, and the components and PCB absorb heat when soldering, making the actual soldering temperature lower.
c) Poor activity of flux or too small specific gravity.
d) Poor solderability of the pad, cartridge hole or pin, which cannot be fully wetted and the resulting air bubbles wrapped in the solder joint.
e) The proportion of tin in the solder is reduced, or the composition of impurities Cu in the solder is high, so that the solder viscosity increases and fluidity becomes poor.
f) Solder residue is too much.
Solution countermeasures.
a) Solder wave temperature 250 +/-5 ℃, welding time 3 ~ 5S.
b) According to the PCB size, board layer, how many components, there is no mount components, etc. Set the preheating temperature, PCB bottom temperature at 90-130.
c) Replace the solder flux or adjust the proper ratio.
d) Improve the processing quality of PCB board, components first come first use, do not store in wet environment.
e) When the proportion of tin <61.4%, add some pure tin in the right amount, and replace the solder when the impurities are too high.
f) The end of each day should clean up the residue.
III. Wave solder joint bridging or short circuit
Causes.
a) PCB design is unreasonable, the pad pitch is too narrow.
b) plug-in component pins are irregular or plug-in skewed, between the pins before welding has been close or has touched.
c) PCB preheating temperature is too low, welding components and PCB heat absorption, so that the actual welding temperature is reduced.
d) too low a soldering temperature or too fast a conveyor belt speed, which reduces the viscosity of the molten solder.
e) Poor activity of solder resist.
Solution countermeasures.
a) Design in accordance with PCB design specifications. The long axis of the two end Chip components should be as vertical as possible with the PCB running direction when soldering
straight, SOT, SOP long axis should be parallel to the PCB running direction. Widen the pad of the last pin of SOP (design a steal tin pad).
b) Inserted component pins should be shaped according to the PCB hole pitch and assembly requirements, such as the use of a short plug once soldering process, soldering surface component pins
Pins exposed PCB surface 0.8 ~ 3mm, insertion requires the component body end square.
c) According to the PCB size, board layer, how many components, there is no placement components and so on set preheating temperature, PCB bottom surface temperature in 90-130.
d) Solder wave temperature 250+/-5℃, soldering time 3~5S. When the temperature is slightly low, the conveyor speed should be adjusted slower.
f) Replace the flux.
IV. Wave soldering spot wetting, leakage, false soldering
Causes.
a) Component solder end, pin, printed board substrate pad oxidation or pollution, or PCB moisture.
b) Chip component end metal electrode adhesion is poor or the use of single-layer electrode, the phenomenon of decapitation in the welding temperature.
c) PCB design is unreasonable, shadow effect during wave soldering causes leakage.
d) PCB warpage, so that the PCB warped position and wave soldering contact is poor.
e) Transfer belt is not parallel on both sides (especially when using PCB transfer frame), so that the PCB and wave contact is not parallel.
f) Wave crest is not smooth, the height of both sides of the wave crest is not parallel, especially the electromagnetic pump wave soldering machine tin wave nozzle, if blocked by oxide
If the wave is blocked by oxides, it will make the wave appear jagged, easily causing leakage and false soldering.
g) Poor flux activity, resulting in poor wetting.
h) PCB preheating temperature is too high, so that flux carbonization, loss of activity, resulting in poor wetting.
Solution countermeasures.
a) Components are used first, do not exist in a humid environment, and do not exceed the specified use date. Clean the PCB and
de-moistening process.
b) Wave soldering should choose the surface mount components with three-layer end structure, the component body and the solder end can withstand more than two times of 260℃ wave
The temperature impact of wave soldering.
c) SMD/SMC adopts wave soldering when the layout and layout direction of components should follow the principle that smaller components are in front and avoid blocking each other as much as possible.
principle. In addition, you can also appropriately lengthen the remaining pad length after the component lap.
d) PCB board warpage less than 0.8 ~ 1.0%.
e) Adjust the lateral level of the wave soldering machine and transfer belt or PCB transfer frame.
f) Clean the wave nozzle.
g) Replace flux.
h) Set the proper preheating temperature.
V. Wave soldering point pulling tip
Causes.
a) PCB preheating temperature is too low, so that the PCB and components temperature is low, the components and PCB heat absorption during welding.
b) Welding temperature is too low or conveyor belt speed is too fast, so that the viscosity of the molten solder is too large.
c) The wave height of the electromagnetic pump wave soldering machine is too high or the pins are too long, so that the bottom of the pins cannot contact with the wave. Because the electromagnetic pump wave soldering machine is a hollow wave, the thickness of the hollow wave is 4 to 5 mm.
d) Poor flux activity.
e) Welding components lead diameter and cartridge hole ratio is not correct, cartridge hole is too large, large pad heat absorption.
Solution countermeasures.
a) According to the PCB, board layer, how many components, have no placement components, etc. set the preheating temperature, preheating temperature at 90-130 ℃.
b) Tin wave temperature is 250+/-5℃, welding time 3～5S. When the temperature is slightly low, the conveyor speed should be adjusted slowly some.
c) Wave height is generally controlled at 2/3 of the PCB thickness. Inserted component pin forming requires the pin to be exposed to the PCB welding surface 0.8 ~ 3mm.
d) Replacement of flux.
e) cartridge hole aperture than the lead diameter of 0.15 ~ 0.4mm (fine lead to take the lower limit, thick lead to take the upper line).
VI. Other wave soldering defects to solve
a) Board surface dirty: mainly due to high solid content of flux, too much coating, preheating temperature is too high or too low, or due to the transmission
too dirty belt claws, too much oxide and tin slag in the solder pot, etc.
b) PCB deformation: generally occurs in large size PCBs, due to the large weight of large size PCBs or due to uneven arrangement of components resulting in
weight imbalance. This requires PCB design to try to make the components distributed evenly in the middle of the large size PCB design process edge.
c) Off the piece (lost piece): poor quality placement adhesive, or placement adhesive curing temperature is not correct, curing temperature is too high or too low will reduce the adhesion strength, wave welding when Connection strength, wave soldering when cannot withstand high temperature impact and wave shear force, make the placement element fall in the material pot.
d) Can't see the defect: solder joint grain size, solder joint internal stress, solder joint internal crack, solder joint brittle, solder joint strength poor, etc., need X-ray, solder joint fatigue test, etc. detection. These defects are mainly related to factors such as solder material, adhesion of PCB pads, solderability of component solder ends or pins and temperature profile.
