Generic Performance Specification for Printed Boards
|Publication Date:||1 July 1996|
Statement of Scope
This specification establishes the general requirements for printed boards and the quality and reliability assurance requirements that must be met for their acquisition. The intent of this specification is to allow the Printed Board user and supplier flexibility to develop optimum procedures for the Manufacture and Procurement of Printed Boards.
Three general classes have been established to reflect progressive increases in sophistication, functional performance requirements and testing/inspection frequency. It should be recognized that there may be an overlap of equipment categories in different classes. The user has the responsibility to specify in the contract or purchase order the performance class required for each product and shall indicate any exceptions to specific parameters, where appropriate.
Class 1 General Electronic Products - Includes consumer products, some computer and computer peripherals suitable for applications where cosmetic imperfections are not important and the major requirement is function of the completed printed board.
Class 2 Dedicated Service Electronic Products - Includes communications equipment, sophisticated business machines, instruments where high performance and extended life is required and for which uninterrupted service is desired but not critical. Certain cosmetic imperfections are allowed.
Class 3 High Reliability Electronic Products - Includes the equipment and products where continued performance or performance on demand is critical. Equipment downtime cannot be tolerated and must function when required such as in life support items or flight control systems. Printed boards in this class are suitable for applications where high levels of assurance are required and service is essential.
Dimensions and Tolerances
All dimensions and tolerances specified herein are applicable only to the end product. Dimensions are expressed in millimeters. Users are cautioned to employ a single system and not intermix metric and inch-based equivalents. Reference information is shown in parentheses ( ).
Acceptability When Limiting Values Are Specified
Specified limiting values of 63.5 mm maximum, 63.50 mm maximum, and 63.500 mm maximum are taken to mean that, for the purposes of determining conformance to this specification, an observed value shall be rounded off to the nearest 0.1 mm, 0.01 mm, 0.001 mm if metric units are used [to the nearest 0.1 inch, 0.01 inch, 0.001 inch if English units are used], and compared to the specified limiting value. Rounding applies to both maximum and minimum values.
When a figure is to be rounded to fewer digits than the total number available, the procedure shall be as follows:
a) When the first digit discarded is less than 5, the last digit retained should not be changed. For example, 3.4634, if rounded to 4 digits would be 3.463; if rounded to three digits, 3.46.
b) When the first digit discarded is greater than 5, or if it is a 5 followed by at least one digit other than 0, the last digit retained should be increased by one unit. For example 8.37652, if rounded to four digits would be 8.377; if rounded to three digits, 8.38.
c) When the first digit to be discarded is exactly 5, followed only by zeros, the last digit retained should be rounded upward if it is an odd number, but no adjustment made if it is an even number. For example, 4.365, when rounded to three digits, becomes 4.36. The number 4.355 would also round to the same value 4.36, if rounded to three digits.
The final rounded figure shall be obtained from the most precise value available and not from a series of successive roundings.
''Shall,'' the emphatic form of the verb, is used throughout this specification whenever a requirement is intended to express a provision that is binding. Deviation from a ''shall'' requirement may be considered if sufficient data is supplied to justify the exception.
The words ''should'' and ''may'' are used whenever it is necessary to express non-mandatory provisions.
''Will'' is used to express a declaration of purpose. To assist the reader, the word ''shall'' is presented in bold characters.
In cases where the stated parameters are inappropriate or insufficient, alternate parameters may be agreed upon between vendor and user.