What is a resistance? 
Does capacitance have a unit? 
How is the resistance measured? 
How is the resistance of thick-film circuits designed? 
Is resistance the same as sheet resistance? What is the relationship between the two?

For a rectangle with a length of l, a width of w, and a height of d (which represents the membrane thickness), at this time L = l, S = w * d. Therefore, R = ρ * l / (w * d) = (ρ / d) * (l / w). Letting l = w, then R = (ρ / d), where ρ is the resistivity of the material. At this time, R is the sheet resistance. 
Definition: Given a length of l, a width of w, and a height of d (which represents the film thickness), at this point L = l, S = w * d. Therefore, R = ρ * l / (w * d) = (ρ / d) * (l / w). Letting l = w results in R = (ρ / d), which is the sheet resistance.

The resistance film layer formed by the printing and sintering of the resist paste is used to test its sheet resistance under a specific thickness. What is sheet resistance? Sheet resistance refers to the resistance between the edges of a square-shaped resist thick film. As shown in Figure 1, it is the resistance value between edge B and edge C. Sheet resistance has a characteristic that the resistance of any size square is the same at the edge-to-edge distance under a specific thickness, regardless of whether the edge length is 1 meter or 0.1 meter, their sheet resistance is the same. For the thick film resistance industry, we generally define the thickness as 10 microns, and the resistance size of a square with equal length and width is the sheet resistance of the resist paste. 
So the resistor that is commonly referred to is the total resistance. The total resistance is the sum of the resistances of all the individual resistors connected in series. 
In simple terms, the aspect ratio resistance is the resistance value of a resistive film with a thickness of 10 micrometers within a square whose length-to-width ratio is 1. 
The unit of specific resistance is Ω/□, which stands for ohm per square. 
When many square resistors are connected in series, they form a resistor. Therefore, the total resistance is the sum of the individual resistances. The total resistance is equal to the length of the resistor body divided by its width, and then multiplied by the number of resistors. 
The design of the resistance circuit should take into account the sheet resistance, the substrate size, and the total resistance value. On a certain-sized substrate, a circuit with appropriate width, length and thickness should be designed. 
The total resistance can be achieved by designing different aspect ratios. Under specific aspect ratios, the total resistance can be changed by adjusting the thickness of the film layer. The total resistance can also be realized by selecting different resistance pastes with different sheet resistances. 

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