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PRINTED CIRCUITS HANDBOOK
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(B) Metallic Mounting Clip
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(A) Insulation Material
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FIGURE 52.4 Component mounting clip insulaton requirements (1) Conductive patterns (2) Metallic mounting clip (3) Insulation material (4) Clearance. (IPC)
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FIGURE 52.5 Component mounting requirements (1) Clip (2) Nonsymmetrical body (3) Top view (4) Center of gravity. (IPC)
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FIGURE 52.6 Bifurcated terminal (1) top edge and (2) base, swaged. Post is broken, but sufficient material is left to attach the specified wires/leads for class I. If both posts are broken, it is unacceptable. (IPC) FIGURE 52.7 Acceptable installed turret terminal and cross section of assembled board. Terminal is intact and straight. (IPC)
ACCEPTABILITY OF PRINTED CIRCUIT BOARD ASSEMBLIES
FIGURE 52.8 Flared flange.Acceptable for all Classes.
After swaging, the area should be free of circumferential splits or cracks. It may have a maximum of three radial splits or cracks, provided that the splits or cracks are separated by at least 90 and do not extend into the barrel of the rivet or funnel (see Fig. 52.9). 52.3.1.5 Connectors, Handles, Extractors, and Latches. Ejectors, handles, and connectors should not exhibit any cracks in the component material emanating from the roll pin or rivet that mounts the component to the PCBA. Roll pins should not protrude more than 0.015 in. from the surface of the ejector, handle, or connector. The major consideration for roll pins should be to ensure that any protrusion does not mechanically interfere with any other assembly. Damage to the part, PCB, or securing hardware is unacceptable.
(b) FIGURE 52.9 (a) Shows an example of acceptable flared swage-split while (b) shows an unacceptable split into barrel.
PRINTED CIRCUITS HANDBOOK
Connector damage can also affect the pins of the connector being pushed or bent out of specification. When connectors are mated, there is the chance that the female portion of the connector pin will be pushed backward and bent. This prevents adequate contact area between the male and female pins of the connector, if they will mate at all. This circumstance is an unacceptable condition. The male connector pins might also be bent. When the male pin is bent significantly, the mating of the female and male connectors can cause mechanical damage to the connector casing due to the male pin being forced into the wrong female connector slot. In most cases, the damage is deformation, cracking, or breaking of the connector casing material, all of which are unacceptable. When connector pins are installed (such as compliant pin, press fit), the pins must be straight within 50 percent of the pin thickness from the perpendicular. For Class 1 and 2 equipment, the PCB land may be lifted less than or equal to 75 percent of the annular ring width. Any land that is lifted across more than 75 percent of the annular ring or has been fractured is unacceptable. For Class 3 equipment, no lifted or fractured lands are acceptable. For all classes, visibly twisted pins, damaged pins, or pins inserted such that there is a nonstandard pin height beyond a specified engineering tolerance is unacceptable. 52.3.1.6 Faceplates. Faceplates must be clean and free of scratches or damage on the front surface. This is important since this is the surface that is commonly viewed by the customer and presents the cosmetic appeal to the product being purchased. An exaggerated example of this is the purchase of an automobile. Few if any consumers would be willing to accept a new automobile with noticeable scratches in the painted surface. A good rule of thumb for scratch criteria that some companies have adopted as a workmanship standard includes the following: 1. A scratch must be visible when viewed under the following conditions to be considered a defect: a. From a distance of 18 in. b. With no magnification utilized c. With normal room lighting used in the assembly area 2. A scratch must be visible from more than one angle to be considered a defect. 3. Metal or plastic faceplate scratches that exceed 0.125 in. in length are considered defects. Surfaces exposed to frequent viewing should be free of blisters, runs, nicks, gouges, blemishes, or other abrasions that would detract from the general appearance of the finish. Faceplates must also be securely fastened to the PCB, that is, tightly enough to prevent physical movement. 52.3.1.7 Stiffeners. Stiffeners are commonly used on PCBA designs that are large in dimension to prevent warpage of the PCBA before, during, or after assembly operations. If a stiffener has kept a PCBA from warping outside acceptability criteria, it has done its job; however, the stiffener must meet the following criteria to be acceptable:
Any marking or color coatings must be permanent. Loss of marking such that it is not legible, or fading or loss of color outside the color standard being used, is unacceptable. The stiffener must be properly seated and mechanically fastened. If the soldering operation is used to mechanically fasten the stiffener to the PCBA, then good wetting to the stiffener such that the stiffener is mechanically sound is required. It is unacceptable to have a loose stiffener on a PCBA.The stiffener must be securely fastened to the PCBA.
52.3.2 Electrical Clearance Electrical clearance of hardware to components or electrical traces must be controlled by the design based on the expected voltage and environment s exposure.As a default, design standards
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