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I'm beginner in electronics.
I want to make footprint of HV5622 shift register using Eagle cad. But I don't know how to set the pad spacing and pad size of the footprint.
There are three values in the datasheet: min, nom, max. I don't know which one to use.
And, in the datasheet, the leg length of the chip is 1.95mm, but I don't know how to set the length of the pad.
There are three values in the datasheet: min, nom, max. I don't know which one to use
Use nominal values (+ 0.2mm) to make your pad. The pitch is 1.27mm. You have enough space to increase the width.
And, in the datasheet, the leg length of the chip is 1.95mm, but I don't know how to set the length of the pad
In this case, I'd say you should increase the length of your pad (by 0.8 to 1mm, I guess) since that wouldn't interfere with the pitch of your device.
PS: Once you have designed the land pattern, review and measure all the dimensions just to be sure. :)
You use the nominal value for the pitch. For most modern parts with anything finer than 50 mil pitch, you usually make the pad and space width the same.
You should use the worst case for both ends of the other dimension. There is no point leaving extra space on the inside end of the pad under the IC. I usually add about 20 mil (½ mm) to the outside ends of the pads if manual soldering is going to be used. It also helps with rework and placing scope probes. It doesn't hurt with reflow soldering as long as the extra area is symmetric, and the surface tension therefore won't pull the package off its footprint when the solder is molten.
Most packages are standardised. If the datasheet does not specify the land pattern, you can usually get it from another part with the same package. For example, there's a complete specification for your PQFP44 package here:
http://www.onsemi.com/pub/Collateral/122BK.PDF
Bear in mind these will usually be specified for reflow soldering, so the pad dimensions may be tight for hand soldering.
