What is flat transformer

Flat transformer, as the name suggests, is a flat type transformer, also known as a flat transformer. Flat transformer performance is outstanding, the use of more and more widely, mainly has the following advantages:
 
1. Large surface area, so good heat dissipation performance, can obtain greater current and power density;
 
2. Low loss, high efficiency, generally up to more than 98%;
 
3. The lamination design can improve the magnetic coupling ability between windings, and the leakage is small;
 
4. Low height, small size, usually 8 to 10 times smaller than the same type of traditional winding transformer;
 
5. Higher switching frequency, can be applied to more than 700KHz working scenarios.
 
 
 
Compared with traditional transformers, the main difference of flat transformers is the difference in the magnetic core and winding.
 
Flat transformer adopts wide width and low height core, such as EIR, EE, EI, POT, etc. Material commonly used 95 materials, with wide temperature, wide frequency, high BS, low loss characteristics, can meet the requirements of high power, high-density use.
 
Flat transformer winding, according to the different structure, can be divided into flat coil, multi-layer PCB board and copper sheet winding.
 
As far as the flat coil is concerned, the spiral method is usually used to wind, and different wire diameters of different sizes and coil inner diameters require separate winding fixtures, and the development cost is high. The pin needs to be removed from the paint on all sides, and it is best to open the pin to make the product of the pin directly, so as to penetrate the tin during welding and improve the reliability of welding.
 
 
 
In addition, when designing the flat coil, pay attention to the width to thickness ratio of the wire, the conventional selection of width to thickness ratio 10 ~ 12, when the width to thickness ratio is greater than 15, the coil inner diameter is prone to line folds, resulting in insulation damage and other problems, which should be paid attention to in the design.
 
For PCB board, the common substrate is FR4 copper clad plate, copper thickness of 1OZ ~ 5OZ (OZ is the common unit of PCB thickness, 1OZ thickness is 0.035mm). Metal pad hole copper thickness should be greater than 25um, more than 3OZ thick copper, hole copper thickness should be greater than 35um. The surface of the pad hole of the multi-layer plate should be as far as possible by gold sinking process, gold thickness 0.05um ~ 0.075um.
 

 
The copper sheet winding is made of pure copper strip cutting or die stamping. The copper grade is usually C1100 or T2 copper. After processing, nickel plating or tin plating is required.
 
In order to ensure the insulation performance of copper sheet winding, polyimide film is often coated on its surface, and high temperature and high pressure curing molding is used to meet the pressure resistance requirements of the product.