Tom
12-05-2002, 05:23 PM
IPC Advanced Study Guide Page Reference: Page 268 & 269, Section 5.1
The producibility levels should not to be interpreted as a design requirement, but a method of communicating the degree of difficulty of a feature between design and fabrication/assembly facilities. The use of one level for a specific feature does not mean that other features must be of the same level. Selection should always be based on the minimum need, while recognizing that the precision, performance, conductive pattern density, equipment, assembly and testing requirements determine the design producibility
Another element of tolerance conditions is the jargon used to define the various characterizations associated with the dimensions and tolerances. In order to do a proper assessment of the physical parameters these definitions need to be completely understood.
Limits of Size The specified maximum and minimum sizes.
Least Material Condition (LMC) The condition in which a feature of size contains the least amount of material within the stated limits of size; for example, maximum hole diameter, or minimum printed board size.
Maximum Material Condition (MMC) The condition in which a feature of size contains the maximum amount of material within the stated limits of size; for example, minimum hole diameter, maximum printed board size.
Tolerance The total amount by which a specific dimension is permitted to vary. The tolerance is the difference between the maximum and minimum limits.
Tolerance, Statistical A tolerance that is based on statistical models, usually combining a variety of specific tolerances i.e. Root Mean Square (RMS) value.
Positional Tolerance The amount that a feature is permitted to vary from the location of true position.
True Position The theoretically exact location of a feature established by basic dimensions.
Dimension A numerical value expressed in appropriate units of measure and indicated on a drawing and in other documents along with lines, symbols and notes to define the size, location or geometric characteristic of a printed board or printed board feature.
Toleranced Dimension A dimension with a directly applied tolerance as opposed to a basic dimension that specifies the exact size or location of a feature.
End Product (End Item) An end product is the individual printed board or assembly in its final or completed state.
Fabrication Allowance An amount added to a printed board feature, e.g. the diameter of a land, which is an accumulation of manufacturing variation. The fabrication allowance is intended to assure that manufacturing variation does not allow certain performance characteristics to be exceeded, such as minimum annular ring.
Basic Dimension A numerical value used to describe the theoretically exact size, profile, orientation, or location of a feature or datum target. It is the basis from which permissible variations are established by tolerances on other dimensions, in notes, or in feature control frames
Bilateral Tolerance A tolerance in which variation is permitted in both directions from the specified dimension.
Geometric Tolerance The general term applied to the category of tolerances used to control form, profile, orientation, and location.
The producibility levels should not to be interpreted as a design requirement, but a method of communicating the degree of difficulty of a feature between design and fabrication/assembly facilities. The use of one level for a specific feature does not mean that other features must be of the same level. Selection should always be based on the minimum need, while recognizing that the precision, performance, conductive pattern density, equipment, assembly and testing requirements determine the design producibility
Another element of tolerance conditions is the jargon used to define the various characterizations associated with the dimensions and tolerances. In order to do a proper assessment of the physical parameters these definitions need to be completely understood.
Limits of Size The specified maximum and minimum sizes.
Least Material Condition (LMC) The condition in which a feature of size contains the least amount of material within the stated limits of size; for example, maximum hole diameter, or minimum printed board size.
Maximum Material Condition (MMC) The condition in which a feature of size contains the maximum amount of material within the stated limits of size; for example, minimum hole diameter, maximum printed board size.
Tolerance The total amount by which a specific dimension is permitted to vary. The tolerance is the difference between the maximum and minimum limits.
Tolerance, Statistical A tolerance that is based on statistical models, usually combining a variety of specific tolerances i.e. Root Mean Square (RMS) value.
Positional Tolerance The amount that a feature is permitted to vary from the location of true position.
True Position The theoretically exact location of a feature established by basic dimensions.
Dimension A numerical value expressed in appropriate units of measure and indicated on a drawing and in other documents along with lines, symbols and notes to define the size, location or geometric characteristic of a printed board or printed board feature.
Toleranced Dimension A dimension with a directly applied tolerance as opposed to a basic dimension that specifies the exact size or location of a feature.
End Product (End Item) An end product is the individual printed board or assembly in its final or completed state.
Fabrication Allowance An amount added to a printed board feature, e.g. the diameter of a land, which is an accumulation of manufacturing variation. The fabrication allowance is intended to assure that manufacturing variation does not allow certain performance characteristics to be exceeded, such as minimum annular ring.
Basic Dimension A numerical value used to describe the theoretically exact size, profile, orientation, or location of a feature or datum target. It is the basis from which permissible variations are established by tolerances on other dimensions, in notes, or in feature control frames
Bilateral Tolerance A tolerance in which variation is permitted in both directions from the specified dimension.
Geometric Tolerance The general term applied to the category of tolerances used to control form, profile, orientation, and location.