Wave crest surface:
Surface waves were covered with a layer of oxide skin, it in along the length direction of solder wave almost static, in the wave soldering process, PCB exposed to tin wave front surface, oxide skin is broken, in front of the PCB solder wave no chap fold is pushed forward, indicating that the oxygen descaling and PCB move at the same speed
Wave soldering machine
Solder joint forming:
When PCB into the wave front side (a), substrate with pins is heated, and before did not leave the wave crest (b), the whole PCB immersed in the solder, solder bridging, but in leaving the moment at the end of the crest, a small amount of solder due to the wetting force, adhesion on the pad and due to the surface tension, appear in order to lead for the contract to minimum state, at this time between the solder and the wetting force greater than the cohesive force of the two bonding pads between the solder. So it will be full, round and round the solder joints, leaving the peak of the tail of excess solder, due to the gravity of the reasons, back to the tin pot.
Prevent bridging
1, the use of good bonding components /PCB
2, to help improve the activity of Ji
3, improve the preheating temperature of PCB, increase the wetting property of the pad
4, improve the temperature of the solder
5, remove harmful impurities, reduce the cohesive force of the solder, in order to facilitate the separation between the two solder.
Preheating method for wave soldering machine
1, air convection heating
2, infrared heater heating
3, the combination of hot air and radiation method of heating
Analysis of wave soldering process curve
1, wetting time
The time of wetting of the solder joint after contact with the solder.
2, residence time
PCB on a solder joint from the contact surface to the peak of the time to leave the peak
3, preheating temperature
Preheat temperature is the temperature that the PCB reaches before the wave crest.
4, welding temperature
Welding temperature is a very important welding parameters and is usually higher than the solder melting point (183 degrees C) 50 DEG C to 60 DEG C, most of the time, is refers to the actual operation of temperature soldering tin furnace, welding of PCB solder joint temperature to below the temperature. This is because the results of PCB endothermic
SMA type components preheating temperature
The single panel assembly through hole devices and mixed 90~100
Two sided plate assembly through hole device 100~110
Double plate assembly of mixed 100~110
Multilayer plate through hole device 115~125
Multilayer mixed 115~125
Parameter adjustment of wave soldering process
1, wave height
Peak height is the PCB in the wave soldering. Its value is generally controlled at the PCB plate thickness of 1/2~2/3, which leads to molten solder flow onto the PCB surface, forming a "bridging""
2, transfer angle
Wave soldering machine at the time of installation in addition to the machine level, adjusting the angle of inclination of the transmission device, through the adjustment of the inclination angle, can control PCB and wave surface welding time, certain angle, will contribute to the strip with the PCB solder liquid faster, returned to the tin pot
3, hot air knife
The so-called hot air knife, SMA had just left the wave soldering, at the bottom of the SMA placed a long and narrow with opening cavity, long and narrow cavity to blow hot air, especially knife shaped, so that "hot knife"
4, the effect of solder purity
In the process of wave soldering, the impurities of the solder are mainly from the copper leaching of PCB, and the excessive copper can lead to the increase of welding defects.
5, flux
6, the coordination of process parameters
The process parameters of wave soldering machine with speed, preheating time, welding time and inclination angle need to coordinate with each other.
Analysis of wave soldering defects:
1 stained with tin bad WETTING: POOR
This situation is not acceptable in the solder joints, only a part of tin. Analysis of the reasons and ways to improve the way such as the next:
1-1. contaminants such as oil, grease, wax, etc., such contaminants are usually available in solvent cleaning, such as when the oil is printed on the dip in the solder.
OIL 1-2.SILICON is usually used for release and lubrication, usually
Found on the substrate and parts of the foot, and OIL SILICON is not easy to clean up, because of the use of it to be very careful, especially when it does not have the problem of oxidation of oil, because it will evaporate dip in the substrate caused by poor dip tin.
1-3. constant
Storage situation is bad or substrate process on the oxidation and flux can not remove will resulting in dip tin side, a second tin or solve the problem.
1-4. flux dip way is not correct, the cause for foaming pressure instability
Fixed or insufficient, resulting in foam height instability or uneven and the substrate part does not stick to the flux.
1-5. eat tin
Less than or Xiwen shortage will resulting in dip tin bad, because of molten tin need adequate temperature and time WETTING usually the solder temperature should be above the melting temperature of 50 DEG C to 80 DEG C, dip tin time about 3 seconds. Adjust the solder paste viscosity.
2 local dip tin:
This situation is stained with tin bad similar and different is local moistens the tin side are not exposed to the surface of copper foil, only a thin layer of tin unable to form full of solder joints.
3 cold solder or disturred solder:
Solder joint appears to be broken, uneven, most of the reasons is parts in the solder was about to cooling formation in the solder joints caused by vibration, delivery note tin whether there is abnormal vibration.
4 solder joint rupture:
This is usually the case of solder, substrate, and through holes, and parts of the expansion coefficient between the feet, not caused by the substrate material, parts and materials to improve the design.
5 solder solder amount is too large:
Usually in the evaluation of a solder joint, hoping to be large and round and fat of the solder joints, but the fact that too large solder joints on the conductivity and tensile strength may not be helpful.
5-1. tin delivery point will not correct the cause of solder is too large, the tilt angle by
1 to 7 degrees by substrate design? #123; the whole, generally about 3.5 degrees angle angle, angle the greater the more thin tin tin angle is smaller and thicker.
5-2. improve the tin bath temperature, lengthen the solder time, so that the excess tin reflow to the tin bath.