ERF Variable |
Description |
rm_d2c
|
Reliability margin for all drill to copper measurements
other than annular ring. Used in the calculation of the DRA attributes. |
is the maximum misregistration permitted by a design while still meeting all other requirements. For example, if a 39 mil hole must be within a 51 mil land, the DRA is +/- 6 mils. Even though this simple example illustrates the concept of DRA, it is not usually that simple in actual design.
is a value that offsets the attained DRA value based on customer requirements. If, in the example given immediately above, a customer requires a 1 mil annular ring on the end product, then your RM is 1.
The standard formula used to calculate the DRA for various tests is:
DRA = (minimum test value) - RM
The formula used to calculate the DRA for annular ring, as an example, would be:
DRA = (annular ring) - RM
In the above example, applying the formula will produce:
DRA = 6 - 1 = 5
This new value of DRA is used as a guideline to determine the difficulty of manufacturing this job and the tolerances that will be forced upon it during the manufacturing process.