How do I read the component dimension labels given in a schematic?

Question

How to read the dimension labels of this IC?

Answer 1

The figures underneath the solid lines are in millimeters, the ones above the line are in inches.

The X.XXX - X.XXX is a range, to account for variations in manufacturing.

So for example, the width shown on the plan view of the chip (top) is given as 0.220 - 0.310 inches. This means that the actual value could be anything in that range. Some chips might be 0.23 ins wide, some might be 0.25 ins wide, etc.

Similarly, there are ± signs after some numbers. For example, the pin spacing on the bottom right elevation is given as 0.100 ± 0.010 ins.

This means that the actual value could be anything in the range between 0.1 - 0.01 ins, and 0.1 + 0.01 ins, i.e. 0.099 - 0.101 ins.

Hope this helps.