The Carbon Oil Process in fact is use the screen printing technology, printed carbon oil in the specified location of the PCB board, after oven cured and tested,formed a carbon film which with certain resistance to instead of the original resistance components. In fact, the production process is the same with the silk screen,to insist on what is the difference, that is, carbon oil has better conductive performance, the silkscreen is only played a welding role.
Carbon oil gap: Because carbon oil has good electrical conductivity, so the carbon plate on the finished board should have a certain gap to ensure that no short the circuit, usually require the min 8mil gap on the finished board (HOZ bottom copper), 12mil gap (1- 3OZ bottom copper), if the production of film can increase the gap, then try to increase the gad at the finished board to ensure that no short circuit.
Carbon oil minimum tolerance: +/- 6 mils
Carbon oil window size and copper gap: consider the tolerance and oil leakage and other factors, carbon oil should bigger 6 mil than copper PAD side(HOZ bottom copper), 8mil (1-3OZ bottom copper), can guarantee not exposed copper.
Carbon oil thickness: silk screen carbon oil thickness: 0.3-1.0mil, tolerance: +/- 0.3mil;
if require carbon oil thickness more than 1.0mil, you need to return the carbon oil twice, The second carbon oil,thickness: 1.0-2.0mil,tolerance: + / – 0.4mil, the second return of carbon oil film should smaller mil than the first silk screen carbon film. So the MI need to write two sets of tools.
Special Carbon Oil Process
1.The operator must wear gloves
2.The equipment must be clean, the surface shall not have dust, garbage and other debris
3.Silk speed and back to the ink speed suction pressure control in the best range. (Based on the printing effect as a test)
4.Screen stencil, scraper, carbon oil specific requirements in accordance with the requirements of engineering MI
5.Carbon oil must be mixing evenly before use, with a viscometer to detect the viscosity within the required range, the ink need timely closure after finish the use.
6.Before printing,all boards must be cleaned plate grease, oxide and other pollutants, all carbon plate carbon plate must be confirmed by the QA before the official production
7.Carbon board drying temperature 150 ℃ time 45 minutes. Carbon oil hole Drying temperature 150 ℃ Time 20 minutes
8.Carbon oil resistance measurement, resistance value of carbon oil should be less than 100 ohms, carbon line resistance should be less than 25Ω
9.After the release from oven, the operator should inform the QA to check the carbon resistance and do the adhesion test.
10.Each carbon oil screen version use max 2500 prints, must be returned to the network room re-drying the new version when up to 2500 times.
At the moment,only very few factories have the carbon oil process,but duke circuit co.,ltd would always provide this service for no only for bulk quantity,but also for PCB prototype.
