[Free PCB Software]

Eagle or KiCad. Now that you are about to order from ALLPCB, you can take a good look at their website. They have recommendations for free PCB CAD software:

https://www.allpcb.com/software/

[How do you get a PCB when you need in your project?]

Maybe you can try to apply a sponsorship for your project. I'm not afficiate with ALLPCB but I heard that they have a good program of  Educational & Engineering PCB Sponsorship. They  have always encouraged  student engineers and professions around the world to innovate.

You also can visit https://www.allpcb.com/sponsor.html to learn more.

[What is tab route?]

A tab route is used to create arrays, often called "route and retain".  Tab routing lets you place more than one board (of either the same or different design) into a given area. This is typically for the convenience of the customer or for assembly requirements that utilize pick and place machines to load components. PCBs are then separated by breaking or cutting the tabs. 

[Capacitor Function]

Hello everyone, as  an electronic enthusiast，i'd like to share some electronic knowledge.

In the circuit, capacitors is to cut off the DC through alternating current, and it is commonly used in inter-stage coupling, filtering, decoupling, bypass and signal tuning.

A. Filter capacitor is used in the power supply rectifier circuit to filter out the AC component. So that the output of the DC  can be  more smooth.

B. Decoupling capacitors are used in the amplifier circuit to eliminate self-excitation to ensure  the amplifier stable operation.

C. Bypass capacitor is used in a resistance connection and connected to the ends of the resistor to pass the AC signal.

D. Decoupling capacitors are mainly removed from high frequency such as RF signal interference, interference is entered by electromagnetic radiation. In fact, the capacitor near the chip also plays the role of energy storage.

E.The high-frequency switching noise is generated by the active device will propagate along the power line. The main function of the decoupling capacitor is to provide a local DC power supply to the active device to reduce the propagation of the switching noise on the board and to direct the noise to ground.