IC Layout: What are I/O Pads and Why are They Necessary?

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In summary: The solution is to use a little metal pad, large enough that the bonder can hit it nearly 100% of the time.- WarrenThis is actually a nomeclature problem in the industry. There are two types of pads: analog pads and digital pads. An 'analog pad' is essentially just a metallic (ohmic) contact, also called simply a 'bond pad.' The term 'digital pad,' however, is sometimes used to refer to both the bond pad AND the digital pad driver and amplifier used for I/O. Analog pads are used more often in analog circuits, while digital pads are more common in digital circuits.
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EvLer
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Does anyone know why I/O pads are necessary in IC layout?
is it because there are input/output signals coming in/out of the chip and one would want to interface it to something else?
Is it really that simple? or I am missing something...
 
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The biggest reason is that the external world is connected to the IC by bond wires. The bond wires, while still thinner than human hairs, are absolutely enormous when compared to IC feature sizes. Futhermore, the bonding machine is not perfect, and doesn't always land its bonding wires in exactly the right spot.

Besides, you need some kind of metallic (ohmic) connection between the chip and the outside world; you can't easily bond a wire to silicon.

The solution is to use a little metal pad, large enough that the bonder can hit it nearly 100% of the time.

- Warren
 
  • #3
ooooooohhh... ok... now i get it... thanks :)
 
  • #4
By the way, you didn't specify whether you're talking about analog or digital pads, but there's a bit of a nomeclature problem in the industry.

An 'analog pad' is essentially just a metallic (ohmic) contact, also called simply a 'bond pad.' The term 'digital pad,' however, is sometimes used to refer to both the bond pad AND the digital pad driver and amplifier used for I/O.

If you're asking "why do ICs need special pad drivers?" then the answer is because off-chip lines have large capacitance, and you need a very large driver, capable of large currents, to quickly charge and discharge that capacitance.

- Warren
 
  • #5
chroot said:
By the way, you didn't specify whether you're talking about analog or digital pads, but there's a bit of a nomeclature problem in the industry.
- Warren
I think I meant 'analog'... and actually did not know about the digital part of it. So, they actually use amplifiers for I/O? thanks for the extra stuff...
 
  • #6
ok, one more thing... I recently did a layout of my chip in SOC encounter and I had to pad it with no-connect pins, i.e. dummy pins. Since the design was presupposing a square chip with 40 pins, 10-N, 10-S, 10-E, 10-W, I padded everything up to 40, I had only 19 I/O proper. However I noticed the pins were spaced out. I ran verify connectivity and did not get any violations. But then when I added more no-connect pins to fill in the spacing around the core I got 600-some connectivity violations. How do I fix this?
 
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  • #7
I hope you ran place & route again after you laid down your dummy pads?

- Warren
 

1. What are I/O pads in IC layout?

I/O pads, also known as input/output pads, are the interface between the integrated circuit (IC) and the outside world. They are the physical connection points for signals to enter and leave the IC.

2. Why are I/O pads necessary?

I/O pads are necessary for the proper functioning of an IC. They allow for signals to be transmitted to and from the IC, enabling it to interact with other components and systems.

3. What are the key features of I/O pads?

The key features of I/O pads include bond pads, which are used for wire bonding to the IC package, and power pads, which provide the necessary power supply to the IC. I/O pads also include input and output buffer circuits, which are used to interface with external devices.

4. How are I/O pads designed in IC layout?

I/O pads are designed in the IC layout using a combination of standard cells and custom layout techniques. The pad frame, which includes the bond pads and power pads, is typically a standard cell that is replicated multiple times to create a pad ring. The input and output buffers are then custom designed to meet the specific requirements of the IC.

5. Are there different types of I/O pads?

Yes, there are different types of I/O pads, such as digital pads, analog pads, and mixed-signal pads. Digital pads are used for digital signals, while analog pads are used for analog signals. Mixed-signal pads combine both digital and analog functionality.

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