Aug 04 , 2020
In the early days of the electronics industry, before SMT (Surface Mount Technology) was fully developed, almost all circuit board assemblies had to go through this type of "wave soldering" process in order to solder electronic parts to the circuit board.
The reason why it is called "wave soldering" is that it involves the use of a barrel of tin furnace which is heated to a temperature that melts the tin strip and forms a molten tin liquid.
With the advances in industrial technology, most electronic components are getting smaller and smaller and can meet SMT reflow requirements (e.g., small size and high temperature resistance), so most boards today have abandoned this traditional wave soldering process.
However, there are still a few electronic parts that are not SMT ready, so in some cases this solder-intensive process must be used.
This video uses a bubbling flux, which appears to only turn on the Cascade Wave, but uses the Cascade Wave.
The following is a general explanation of wave soldering (see the video), which is basically divided into four parts.
The first part is Flux Zone
The purpose of using Flux is to improve the quality of soldering parts, because circuit boards, electronic components, and even solder liquids may be contaminated by the environment in which they are stored and used, which may cause oxidation and affect the quality of soldering. The main function of the "flux" is to remove oxides and dirt from the metal surface, and to form a thin film on the surface of the metal to insulate the air when operating at high temperatures. However, the wave soldering process must use molten solder as the soldering medium, since it is a liquid solder, then the temperature must be higher than the melting point temperature of the solder to do so, the current SAC305 lead-free solder temperature is about 217 ° C, ordinary flux can not be retained for a long period of time under such high temperatures, so if you want to add flux, you must first before the circuit board has been through the liquid solder. Smearing.
There are two general ways to apply flux, one is to use foaming flux, which will adhere to the circuit board when it passes through the flux zone, the disadvantage of this method is that the flux is often not evenly applied to the circuit board, resulting in the possibility of poor soldering in areas where the flux has not been applied.
The second method of applying flux is the spray coating method, where the nozzle is placed under the chain and sprayed from bottom to top as the board passes through. This method also has the disadvantage that it is easier for the flux to penetrate through the gap on the board, and poor luck may allow the flux to directly contaminate the parts on the front of the board, or even penetrate into the inside of some parts that are more sensitive to flux, resulting in unstable time bombs in the future, or left on the top of the wave soldering machine.
If the flux drips directly onto the board and is left untreated, it is likely to cause quality problems such as board corrosion or micro-circuits.
The reflow process also has flux in the solder paste. It's just that it's not usually easy for us to notice.
The second part is the Pre-Heating Zone
Just like the SMT process, the wave soldering process also needs to pre-heat the circuit board before the actual soldering, this is to reduce the deformation of the circuit board, to avoid some parts of the internal moisture, otherwise, direct rapid heating from room temperature to more than 217 ° C temperature, it will easily cause popcorn (popcorn) or delamination (delamination) and other defects.
If the same as boiled eggs, if you first heat the water to boiling, directly into the boiling hot water into the raw egg, the egg is bound to break, and extruded egg white. To make a perfect boiled egg, drop the egg into cold water and then gradually boil it from cold water.
The third part is the soldering zone
There is a large vat of molten tin that is already heated and melted, which is why it is called a "tin furnace. Since it is a liquid tin, various tin surfaces can be made according to the characteristics of the liquid to meet the needs of the solder.
Generally speaking, the tin bath in a tin furnace is subdivided into two slots, the first called the spur and the second called the stratosphere, each of which has a different function and in most cases only turns on the stratosphere.
The main purpose is to solder SMD parts, because SMD parts are usually densely distributed in various areas of the circuit board, and there are large and small, high and low, because the action of the circuit board is similar to a sampan gliding, so if there is a large object under the sampan, the so-called "shadow effect" will be formed behind the large object when gliding. If there is no tumbling of the solder, it cannot reach the parts or joints underneath the shadows, which will cause soldering problems. However, because the tin is always rolling, the soldering effect is sometimes uneven, and sometimes there is a soldering bridge, so it is usually added after the disturbing wave.
It can effectively eliminate some of the burrs and solder bridge short-circuiting problems caused by the previous "Spoiler". In addition, Smoothing Wave is also very good for soldering traditional through-hole components (long pins protruding from the board), if there are only through-hole components in the wave solder connection, then the Spoiler can be turned off and soldering can be done by Smoothing Wave.
The fourth part is the cooling zone
In this area, a cooling fan is used at the exit of the oven to cool down the board, which has just been exposed to a high-temperature liquid tin, because of the soldering and repair work that needs to be done immediately afterwards. Rapid cooling is not used on boards that have been through a tin furnace, probably because most of them are conventional through-hole components or larger SMD parts.
Some wave ovens have an additional cleaning process behind them, because some boards will still go through the cleaning process.
Why do we need a tilt angle for wave soldering?
I believe you should have noticed that the track of "wave soldering" and the tin surface has a certain tilt angle, the general tilt angle is set at about 3 ~ 7 °, the reason for a slight tilt is to facilitate the removal of solder joints from the tin surface, and this tilt angle is also called the "desoldering angle". When the PCB board and the liquid molten solder surface are separated from each other when over-tinning, an angle is needed, and the smaller this angle is, the larger the solder joint will be, and vice versa.
The smaller the de tin angle is, the larger the solder joint will be, and vice versa. If there is no inclination between the track and the tin surface during "wave soldering" and no de tin angle, the solder joint will be too large, and a large amount of continuous tin will easily appear.
Selective wave soldering
Because not all parts on the current circuit board need to be wave soldered, often there are hundreds of parts on a board, but only less than five parts need to be wave soldered, so the process of selective wave soldering has been extended.
Selective wave soldering is divided into two ways.
The first type of selective wave soldering is to use wave soldering overheater carriers to cover up the parts that do not need wave soldering and still use the original wave soldering process.
The second type of selective wave soldering is to use a small nozzle such as a small tin stove, and then move the nozzle to aim at the part to be soldered.