| 4.1.1
Printed wiring board design (1/3 Page)
|
| (1) Diameter of DIP through
hole |
|
This section describes
the relationship between the pin positional tolerance and the pin existence range, using the package
drawing of an 8-pin plastic DIP package as an example. |
 |
|
 |
 |
| Figure 4-1. Package
Drawing of 8-Pin Plastic DIP (7.62mm(300)) |
|
The precision of the
package pins in this diagram is guaranteed from the positional tolerance indicated by the logically
accurate dimensions (dimension of square circumference: pin row interval/pitch), pin width/thickness
tolerance, and pin position variation range. |
[ Logically accurate dimensions
]
[ Pin width/thickness tolerance ]
[ positional tolerance: indicating the range
of shift of the pin center position ]
 |
Table 4-1. Description
of Geometrical Tolerance
|
Symbol indicating the positional
tolerance. |
|
Numerical value indicating
that the positional tolerance of the pin center is in the range of x = 0.25 mm.
Allowable range that each pin center can deviate from the logically accurate dimensions when parallel
chucking is performed at a pin row interval of 
= 7.62 mm for both pin rows of the DIP package. |
|
Symbol indicating that the
positional tolerance can be up to x = 25 mm, based on a pin width of b MAX = 0.60 mm.(i.e. If the pin
width b is less than the maximum value, the tolerance will be greater than x = 0.25 mm) |
|
According to these setting
values, the pin existence area is within the range determined by a pin positional tolerance of x = 0.25
mm when the pin row interval
= 7.62 mm (300 mils) + pin pitch.
A concrete calculation example is shown below. |
| The allowable existence
area of pin width direction |
|
= 2 x [b MAX./2
+ x/2] = 2 x [0.60/2 + 0.25/2]
= 2 x [0.85/2] = 0.85 mm |
|
This relationship is
shown in Figure 4-2 on the next page. |
|
