According to statistics, in a circuit, the resistance accounts for about 30%, capacitance accounts for about 40%, so that the downstream process of PCB placement and plugging process adds a lot of trouble. As a result of the general resistance to heat power are relatively small, so some people proposed whether the resistance, capacitance compression in the PCB board? Thus buried resistors, buried capacitors came into being.
Buried resistance, also known as buried film resistance, is a special resistive material pressed together on an insulating substrate, and then through printing, etching and other processes to form the design of the required resistance value of the inner (outer) material, and then pressed together in the PCB board (on) to form a flat resistance layer of a technology.
Buried resistance is mainly used for the board can not be laid out or to improve the signal, the general resistance value control accuracy of less than ± 10%. Buried resistance has five advantages.
(1) Advantages in high-density/high-speed transmission circuit design.
Improving the impedance matching of the line.
Shortening the path of signal transmission and reducing parasitic inductance.
Elimination of inductive reactance generated in surface mount or cartridge processes.
Reduction of signal crosstalk, noise and electromagnetic interference.
(2) Advantages in replacing placement resistors.
Reduction of passive components and increased density of active component placement.
Improvement of board wiring capability because of the reduction of lead-through holes.
Because the soldering point is reduced, so the stability of the electrical parts after assembly is improved.
(3) The buried resistor after integration has advantages in stability.
(a) The loss of buried resistors after cold and heat cycles is very low, about 50 × 10-6, while the loss of other discrete resistive components is 100 to 300 × 10-6.
Increase in resistance at about 2% after storage at 110°C for 10,000h.
Stability test in a wide frequency range, less than 20GHz.
(4) The resistor value of various specifications can be synthesized by simply adjusting its form factor, and it can be perfectly matched with the interline inductance.
(5) In the design of high-density discrete resistor components, the use of buried resistor technology can reduce the number of layers and size of the PCB, reducing the quality of the PCB board and manufacturing costs.
At present, the more mature resistor material is Ni-P material, the general P content is about 10%, by adjusting the Ni-P material of different thickness and P content to adjust the resistivity of the material.
The core of the buried resistance process is three etching, copper etching - resistive material etching - copper etching (formation of resistance).
