The ceramic pcb circuit board is actually made of electronic ceramics, and can be made into various shapes. It is applied to the LED field, high-power power semiconductor module, semiconductor Coolers, electronic heaters, power control circuits, power mixing circuits, smart power components, high frequency switching power supplies, solid state relays, automotive electronics, communications, aerospace and military electronic components.
- Higher thermal conductivity
- More matching coefficient of thermal expansion
- A harder, lower resistance metal film aluminum oxide ceramic circuit board
- The solderability of the substrate is good and the use temperature is high.
- Good insulation
- Low frequency loss
- Can be assembled in high density
- Free of organic components, resistant to cosmic rays, high reliability in aerospace and long service life.
Ceramic circuit board process – etching
A layer of lead-tin resist is pre-plated on the copper foil that needs to be retained on the outer layer of the board, and then the unprotected non-conductor portion of the copper is chemically etched away to form an electrical circuit.
According to different process methods, etching is divided into inner layer etching and outer layer etching, inner layer etching is acid etching, wet film or dry film is used as resist; outer layer etching is alkaline etching, and tin-lead is used as resist. .
Basic principle of etching reaction
1. Acidic copper chloride etching
Developing: The portion of the dry film that is not irradiated with ultraviolet light is dissolved by the weak alkalinity of sodium carbonate, and the already irradiated portion remains.
Etching: According to a certain proportion of the solution, the copper surface exposed by dissolving the dry film or the wet film is dissolved and etched away with an acidic copper chloride etching solution.
Stripping: The protective film on the line is dissolved according to a certain proportion of the potion at a specific temperature and speed.
Acidic copper chloride etching has the characteristics of easy control of etching speed, high efficiency of copper etching, good quality, and easy recycling of etching liquid.
3. Alkaline etching
Stripping: The film is removed from the surface of the circuit board by using phoenix liquid to expose the unprocessed copper surface.
Etching: The unwanted underlying copper is etched away with an etchant solution, leaving a thickened line. Among them, auxiliaries will be used. The accelerator is used to promote the oxidation reaction to prevent the precipitation of cuprous mis-ions; the repellent is used to reduce the side erosion; the suppressor is used to suppress the flow of ammonia, precipitate copper and accelerate the oxidation of copper.
New lotion: Use ammonia monohydrate containing no copper ions, and remove the residual liquid on the board surface with ammonium chloride solution.
Conditioning: This procedure is only applicable to the immersion gold pcb process. The excess palladium ions in the non-plated through holes are mainly removed to prevent gold ions from sinking in the gold sinking process.
Solder stripping: The tin-lead layer is removed using a nitric acid solution.
Four effects of etching
- Pool effect
During the etching process, the liquid will form a water film on the plate due to gravity, which hinders the contact of the new liquid with the copper surface.
- Ditch effect
The adhesion of the drug solution causes the drug solution to adhere to the gap between the line and the line, which can result in different etching amounts in the dense area and the open area.
- Via effect
The liquid medicine flows down through the hole, which leads to an increase in the speed of renewing the liquid medicine around the plate hole during etching, and the etching amount is increased.
- Nozzle swing effect
The line parallel to the swing direction of the nozzle, because the liquid medicine between the lines is easily dissipated by the new liquid medicine, the liquid medicine is refreshed quickly, and the etching amount is large;
The line perpendicular to the direction in which the nozzle swings, because the liquid medicine between the lines is not easily dissipated by the new chemical liquid, the liquid medicine is refreshed at a slow rate, and the etching amount is small.
Common problems in etching process and improvement methods
- The film is not exhausted
Because the concentration of the syrup is too low; the speed of the line is too fast; problems such as nozzle clogging can cause the film to endlessly. Therefore, it is necessary to check the concentration of the syrup, and adjust the concentration of the syrup to an appropriate range; adjust the speed and parameters in time; and clear the nozzle.
- Surface oxidation
Because the concentration of the syrup is too high, the temperature will be too high, which will lead to oxidation of the surface of the board. Therefore, it is necessary to adjust the concentration and temperature of the syrup in time.
The copper is not finished
Because the etching speed is too fast; the composition of the syrup is biased; the copper surface is contaminated; the nozzle is clogged; the temperature is low, and the copper etch is not completed. Therefore, it is necessary to adjust the etching transport speed; re-check the composition of the syrup; be careful of copper contamination; clean the nozzle to prevent clogging; adjust the temperature.
The copper is too high
Because the machine runs too slowly, the temperature is too high, etc., which can lead to excessive copper corrosion. Therefore, measures such as adjusting the machine speed and adjusting the temperature should be taken.