Wave crest:
the surface of a wave is covered by a layer of oxide that remains almost stationary along the length of the solder wave, In the process of wave soldering, PCB contact to the front surface of tin wave, oxide breakdown, tin wave in front of the PCB without certain fold, being pushed forward, this indicates that the entire oxide skin moves with the PCB at the same speed as the wave soldering machine.

Solder forming: 
When the PCB enters the wave front (A), the substrate and the pin are heated and left the crest surface (B) before the entire PCB was immersed in solder, that is bridged by solder, but at the moment of departure from the end of the wave crest, a small amount the solder is adhered to the pad due to the wetting force, and the wire is centered as a result of surface tension shrink to the minimum state where the wetting force between the solder and the pad is greater than the cohesion of the solder between the two pads. So it will form
the full, rounded solder joints leave the excess solder at the end of the crest and fall back into the tin due to gravity.

Prevent bridging from occurring
1, using good solderability components/PCB
2, to help improve the activity of Ji
3, Increase the preheating temperature of PCB and increase the wettability of the pad
4, Increase the solder temperature
5, Remove harmful impurities, reduce the cohesion of solder, in order to facilitate the separation of solder between the two solder joints.

Preheating method commonly used in wave soldering machine
1, Air convection heating
2, Infrared heater heating
3, Heating by combining hot air with radiation

Analysis of wave soldering process curve
1, Wetting time: refers to the solder joint and solder contact after wetting start time
2, residence time: PCB on a solder joint, from contact wave crest surface to leave the wave surface time, stay/welding time calculation method.
Type: dwell / weld time=crest width/ speed
3, Prheat temperature: preheat temperature means the temperature reached by PCB before contact with wave crest(see table on the right)
4, Welding temperature
Welding temperature is very important, welding parameters are usually higher than the solder melting point (183 degrees C), 50 degress C, ~60 degress C most.
The situation refers to the temperature of the soldering furnace. In actual operation, the welding temperature of the PCB solder joint is lower than the furnance temperature, because PCB.

Endothermic results
Preheating temperature of type SMA component
The single panel assembly through hole devices and mixed 90~100
Double sided plate assembly through-hole device 10~110
Double plate assembly of mixed 100~110
Multilayer through hole device 15~125
Multilayer mixed 115~125

Adjustment of wave soldering process parameters
1, Crest height: wave height refers to the wave soldering PCB, tin height. Its values are usually controlled by the thickness of the PCB plaste
The 1/2 ~2/3 assembly leads to molten solder following to the surface of the PCB to form a bridge
2, Transmission angle: wave soldering machine in the installation, in addition to the machine level, but also should adjust the transmission device angle, through the tilt angle
The regulation can control the welding time between the PCB and the wave crest, and the proper dip angle will help the solder liquid to be faster with the PCB peel off and return to the tin pot.
3, Hot air knife: the so-called hot air knife, is SMA just leave the welding wave crest, in SMA below placed a narrow long belt open the narrow cavity of the mouth can blow out hot air, especially the knife, so it is called " hot wind knife"
4, The influence of the purity of solder: during wave soldering, the impurity of solder mainly comes from copper leaching on the pad of PCB, the amount of copper will cause more welding defects.
5, Flux
6, Process parameters coordination: wave soldering machine process parameters, with speed, preheating time, wleding time and tilt angle between the need for mutual assistance.

Adjust
Analysis of wave soldering defects"
1, dip tin bad poor wetting"
this situation is unacceptable. there is only a part of solder on solder joints. The reason and improvement are as follows:
1-1 outside pollutants such as oil, grease, wax, etc., such pollutants are usually cleaned with solvents, such oils are sometimes printed, welded
When the agent is stained

1-2 silicon oil is usually used for stripping and lubrication, usually found on the substrate and parts of the foot, and silicon oil is not easy to clean up, so it's very careful to use it, especially when it does antioxidant oil, which often causes problems because it evaporates causing poor tin penetration on the substrate.

1-3. Often oxidizes because of poor storage conditions or problems in the substrate process, which can cause poor solder penetration when soldering flux is not removed, Two times tin or this problem can be solved.

The reason that the 1-4. flux is incorrect is that the foam pressure is unstable or insufficient, which makes the foam
height unstable or uneven.
Do not touch the soldering flux to the substrate

1-5. tin time is insufficient or sivin will result in insufficient tin bad, because the temperature and time of molten tin need enough wetting, the solder temperature is usually higher than the melting point. The temperature is between 50 and 80 degrees. The total time of soldering tin is about 3 seconds. The paste viscosity is adjusted.

2, parts with tin poor: this situation is similar to the tin paste, the difference is that the local poor tin, copper foil surface will not show, only thin A thin layer of tin cannot form a full solder joint.

3, Cold solder or disturred solder joints: seemingly broken, uneven, most of the reason is the vibration in the solder to form parts cooling pads. Due attention, if there is abnormal vibration. Tin transportation.

4, Solder joint repture: this situation is usually caused by the expansion coefficient of the solder, the substrate, the through hole, and the part of the foot, board material, parts, material and design to improve.

5, Solder tin is too large: usually in the evaluation of a solder joint, hope to be large, round and fat spot, but in fact, too much solder joints, electrical conductivity and tensile strenght may not be helpful.
5-1. Tin delivery point will not correct the cause of solder is too large, the tilt angle from 1 to 7 degrees by substrate #123: the whole design, general?

The angle is about 3.5 degrees. The larger the angle is, the thinner the dip is and the smaller the angle is. The thicker the tin.

5-2. increse the bath temperature and prolong the soldering time to return the excess tin to the tin bath.
5-3, Can be reduced by increasing the preheating temperature, soldering heat required by the substrate, have effect on welding.
5-4, Change the proportion of flux, slightly reduce the proportion of flux, usually the proportion of higher, the more thick tin eat, the more likely to short-circuit, the lower the proportion of tin. The thinner, but the easier it is to make the tin bridge and the tin tip.

6, Point of tin
This problem usually occurs on DIP or WIVE welding processes where ice tip tin is found at the top of the part or on the solder joint.
The weldability of 6-1, substrate is poor, and this problem is usually accompanied by poor solder penetration. This problem should be discussed by the weldability of substrate. The lifting flux is improved over time.
On the 6-2, substrate, the gold channel (PAD) area is too large, and the green(solder proof) paint line can be used to separate the gold strip to improve the principle, and the green(solder) paint line is used in principle.
The golden channel is divided into 5mm and 10mm blocks
6-3, tin bath temperature is not enough, tin time is too short, can be increased tin bath temperature, extended solder time, so that excess tin and then reflow to the tin groove 

To improve
6-4, after the peak of the cooling air flow angle is not, not to the tin groove direction blowing, tin will cause rapid point, the excess solder can not be gravity.
The cohesive force is brought back to the tin groove
6-5. Solder tip produced when soldering, usually the soldering iron temperature is too low, the solder temperature is not enough, can not immediately due to cohesion retraction formed solder joints.
Use a larger wattage soldering iron to lengthen the preheat time of the soldering iron on the soldered object.
7, solder on the green paint left with residual tin:
7-1, made some residual substrate material can not be compatible with the flux, in overheating, after nunan produce viscous adhesive solder shape, Cheng xisi can be cleaned with acetone(** chemical solvents that have been banned by the Montreal convention), cholorinated olefins, etc.
If there is no improvement, there is a possibility that the substrate material curing is incorrect. The accident should be promptly returned to the substrate supplier.
7-2. Incorrect substrate curing will cause this phenomenon. It may be first baked 120 hours two hours before the plug-pin provide timely feedback to substrate suppliers. The 7-3. dross is injected into the tin bath by pump and then poured out, resulting in tin dross on the substrate surface. This problem is relatively simple and good tin, tin bath temperature, the correct height(normal condition when the tin groove edge 10mm high from the tin bath not jet static tin surface degree)
White residue: after welding or solvent cleaning, white residue is found on the substrate, usually the residue of rosin.
The class material does not affect surface resistance, but the customer does not accept it.

8-1, flux is uaually the main reason for this problem. sometimes it can be improved by using another flux, and rosin flux is often cleaned.
When the day shift, the best way is to seek the flux supplier assistance, they supply their products are more professional.
In the process of making 8-2, substrate, the residual impurities will also produce white spots under long-term storage, and can be cleaned with flux or solvent.
8-3, is not the correct curing will cause the day shife, usually a single batch production, should be timely feedback to the supplier and substrate

Rinse with flux or solvent
The fluxes used in the 8-4, plant are not compatible with the substrate oxide protective layer, which occur on the new substrate supplier or change the flux plant. The supplier shall be assisted when the licence occurs.
8-5. The solvent used in the substrate process changes the substrate material, especially the solution in the nickel plating process.
It is recommended that the shorter the storage time, the better flux has been used for too long aging and has been exposed to air to absorb water vapor deterioration. It is recommended to update the flux(usually foaming flux should be applied).
Weekly updates, immersion fluxes are updated very two weeks, updated with a spray type monthly using the 8-7, rosin flux, solder furnace after only nine parking time too when cleaning, caused the day shift, try to shorten the soldering and cleaning.
The washing time can be improved
The moisture content of 8-8, solvent cleaning of the substrate is too high, reduce cleaning ability and produce the day shift. Should update the solvent.
9, Dark residues and corosion marks: usually black residues occur at the bottom or top of the solder joint. This problem is uslly incorrect, caused by the use of flux or cleaning
9-1. rosin type flux, not immediately cleaned after welding, leaving dark brown residue, as early as possible to wash
9-2, acid flux in the solder joint, causing black corrosion color, and can not be cleaned, this phenomenon is often found in hand welding, use weaker the flux and cleaned as soon as possible.
9-3, organic flux and scorched black class at higher temperatures, confirm the tin bath temperture, with a flux that is resistant to high temperature can be.
10, green residues: green is usually caused by corrosion, especially electronic products, but not entirely, because it is difficult to tell the difference.
Is the patent or other chemical products, but generatlly found green substance should be alert, must immediately identity the resons, especially the species of green substances will become larger and larger and should be noted with the usual cleaning process to improve.
10-1. corrosion problems: usually occurring on bare copper surface or cooper containing alloys, use of non rosin flux, this corrosive substance contains.
The copper iron is therefore  green, and when found in this green corrosion, it can be proved that it is not cleaned properly after using the non rosin flux.
10-2 copper abietates is compound of copper oxide and abietic, acid( a major component of rosin), a substance is green, but not corrosive. It has high insulation and does not affect quality, but customers will not agree to clean it. The residue or substrate of 10-3, presulfate is similar to residue, and green residue will be produced after soldering.