Microelectronics Print Substrates
The exposed screens are mounted into the print machines and ink is loaded onto the screen. The inks may be metals such as gold, silver or platinum, or they may be a glass dielectric insulator or a resistive ink.
The printing inks are made up of flakes of material suspended in an organic liquid carrier. When printed, the substrate with the wet ink pattern is first dried in a belt drier which drives off the volatile elements of the ink leaving a dry ink pattern. The substrates are then fired down a belt furnace to a particular time/temperature profile taking 50 minutes and peaking at 850°C. This process forms very strong oxide bonds between the ink and the substrate. Sometimes several layers can be printed and dried and then fired together.
The process of building up the circuit is a repetitive one, a typical example might be:
- Print 1st gold conductor layer, typically 3-5µm thick. - Dry, - Fire
- Print and dry 3 layers of dielectric and infill (via conductor) to build up a 28-30µm thick insulating layer.
- Print 2nd conductor layer, - Dry, - Co-Fire all previous layers.
- Print and dry 1st resistor decade.
- Test fire a sample of substrates to ensure resistor values are in the correct range.
- Print, Dry and test fire remaining resistor decades. - Fire batch.
- Print, Dry and Fire coverglaze, (resistor and bond protection) at low temperature
Every print stage is 100% inspected to ensure no open or short circuits and quality of print.