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BBS Pavement design. Diplemo mechinical. Mil-hdbk - Package Cushioning Design. Sign up Log in. Web icon An illustration of a computer application window Wayback Machine Texts icon An illustration of an open book. Books Video icon An illustration of two cells of a film strip. Video Audio icon An illustration of an audio speaker.
Audio Software icon An illustration of a 3. Thus, their size is commonly chosen to beeither 4. Dimensional instability, andassociated problems at all stages of fabrication, assembly,test and system fixturing become factors in determiningfinal board size. IPC February a plane perpendicular to the printed board surfaceB Centrality The distance the center of a web is offset from true. E Cutter angle The total angle of a scoring blade. G Printed board thickness Overall printed board thickness to be scored.
This can be achieved using a number of different tech-niques. These include simple scoring, a combination ofrouting and scoring, and a combination of routing plusbreakaway. Scoring is the machining of a shallow, precise V-grooveinto the top and bottom surfaces of the laminate.
It is gen-erally accomplished using CNC equipment. As scoringallows the removal of rails and individual parts from a pal-let, positional accuracy is critical. See Table and Fig-ure for some standard scoring parameters. CIRCUITable Panel Size to Manufacturing Operation RelationshipsOperation Typical Maximum Panel SizeDrill mm x mmScrub, deburr, and most conveyorized finishing equipment mm x openPlating equipment Custom sized, check with fabricatorExposure equipment mm x mmRouting equipment mm x mmScreening equipment mm x mmBare board test mm x mmLaminating press size based on mm x mm press with 50 mm open area onplated edges.
Routing is the process of profiling a pallet or printed board Grid systems are always basic and have no tolerance, and. Typical grid increments are multiples of 0. February IPCbreakaway tabs.
Instead of scoring, a series of holes aredrilled in the tab to facilitate removal. See Figure When printed board features arerequired to be off a grid, they shall be individually dimen-sioned and toleranced on the master drawing. Table Tolerance of Profiles, Cutouts,Tolerances to be applied to profile of a surface:Profile featureLocation where greatest basic location dimension is less than This ultimatelywill help to minimize end-product printed board cost.
The edges of internalcutouts shall be considered as external board edges andmeet all requirements for hole and conductors to edgeclearance see On multilayer printed boards thelocation of lands, clearances, ground planes and other con-ductive pattern features must also be considered. For printed board shape routing, it is recommended that thecutouts and notches allow for a minimum of a 1. Although a minimum internal radius of0. Recommended tolerances for the location andprofile of cutouts and notches are shown in Table ; how-ever, the tolerances specified on the printed board drawingshall accommodate the dimensions and tolerances of themating part.
This can beperformed either by the use of a pin router and template, ora CNC routing machine. Frequently a combination of routing and scoring is used,where both pallet and printed board are routed, leaving asmall connection bridge.
This bridge is then scored tofacilitate removal following test and assembly. Grid systems shall belocated with respect to a minimum of two printed boarddatums. The grid increment shall be specified on the master draw-ing. The choice of grid increment is based on the compo-nent terminal location for through-hole components, and onthe component center for surface mount components.
Component assembly issues shall be in accordance withthe generic standard IPC and as follows:. In gen-eral, no more than three attachments should be made toeach section of a turret or bifurcated terminal. As an excep-tion, bus bar terminals may hold more than three wires orleads per section when specifically designed to hold more. They are generallyused where the amount of force makes it difficult to safelyremove the board without damage to the electrical compo-nents or to the person removing the board.
Extractors are usually of the camming type and aremounted to the corners of the board. They provide amechanical advantage for disengaging the connectors and aconvenient place to grasp the board during removal.
Board extractors may be incorporated into the design of theboard, or may require separate conditions in the printedboard assembly. When board extractors are a part of thedesign, adequate reinforcement shall be used to properlyallow the extracting action to remove the board from itsconnected assembly in the backplane see Figure When board extractors are not a part of the printed boardassembly, an extractor of the gripping variety may be used see Figure They grip the board in a particular area,which shall be kept free of components and circuitry.
If ahook-type board extractor is used, where a hook passesthrough holes in the printed board, and then pulls the boardout, special grommets should be used to reinforce the holestructure to avoid board crazing or cracking. If the actual land diameter chosen is greater than the mini-mum value calculated, the percentage difference betweenthe land diameters must be subtracted from the total webwidth calculation, i.
The total of the thermal relief cross-sectional area dividedby the number of planes connected to the plated-throughhole shall not violate current carrying capacity require-ments for a given hole. If the individual web width violates the intended minimumconductor width it shall be specified on the master draw-ing. When the pitch is very small,designers must remain cognizant of the narrow foil webbetween clearance openings see Figure As the clear-ance area diameter is made larger, the foil web betweenclearance areas becomes smaller.
Designs having verysmall foil webs are less desirable because of their reducedcurrent carrying capability, potential for increased voltagedrop, higher EMI emissions, and reduced thermal dissipat-ing characteristics. It is highly desirable for heat generatingdevices to be heatsinked down through via holes anddissipated across the surface of inner planes.
For these rea-sons the foil web should be as large as possible and over-lapping clearance areas in planes should be avoided. Note: Maximum clearance area diameter in the plane iscalculated by using the formula above and must not exceedthe total available area. Nonfunctional lands need not be used where electricalclearance requirements do not permit, such as groundplanes, voltage planes and thermal planes. For high layercount boards, greater than 10 layers, it is recommended toremove some of the nonfunctional lands in the verticalstack.
Plated-through holes passing through internal con-ductive planes ground, voltage, etc. This tolerance includes tolerances for masterpattern accuracy, material movement, layer registration andfixturing. The diameter of an unsupportedcomponent hole shall be such that the MMC of the leadsubtracted from the MMC of the hole provides a clearancebetween a minimum of 0.
The number of different hole sizes shall be kept to aminimum. When flat ribbon leads are mounted throughunsupported holes, the difference between the nominaldiagonal of the lead and the inside diameter of the unsup-ported hole shall not exceed 0.
Note: Conductor pattern registration may be expressed in terms ofminimum annular ring violation, which establishes manufacturing registrationallowances.
February IPCmore than 0. The relationships between maximumand minimum barrel diameters and wire diameters shall beas shown in Table Both minimum and maxi-mum leads shall be taken into consideration in evaluatingthe finished plated-through hole requirements. If the lead isa ribbon lead, the minimum and maximum diagonal of aflat ribbon lead shall be considered.
Table shows thelimits of the plated-through hole. These limits shall be optimized so that manufacturability isenhanced to provide the most liberal tolerances allowable see Figure Unless otherwise specified, the hole size shall be the fin-ished plated size after solder coating or final plating andfusing, if required. The hole size shall be specified on themaster drawing. Plated-through holes used for functionalinterfacial connections shall not be used for the mountingof devices which put the plated-through hole in compres-sion.
Plated-through holes used for functional interfacialconnections shall not be used for the mounting of eyelets,solder terminals, or rivets. Plated-through holes shall beused for all interfacial connections on multilayer boardsType 3 through Type 6 inclusive.
Platings and coatingsshall be in accordance with IPC Table provides information on theproducibility of aspect ratios for various levels of complex-ity.
Thus, a hole 1. When hole size is less thanone-fourth the basic board thickness, the tolerance shall beincreased by 0. Table providesinformation on the minimum drilled hole to be used inconjunction with various board thicknesses.
The tablereflects the three classes of equipment assuming that eachclass requires a slightly more severe environment, thushaving to meet more stringent thermal cycling conditions see IPC-D If a particular class requires more stringent cycling thanshown in the table, the user may invoke the requirementsof a larger drilled hole size. Solder may fill the through hole or via if processed withfused tin-lead plate or solder coating. Partial filling atassembly can create stress concentrations affecting reliabil-ity.
For drilled hole diameters 0. The drilled hole size used for through hole vias shall berepresented on the master drawing as the maximum plated-through hole dimension that assumes that the hole containsa minimum plating thickness.
No minimum plated-throughhole dimension should be specified since the through-holevia contains no component lead or pin and could theoreti-cally be plated shut. Thus, a master drawing call out of0. In addition, Table contains a letter code in each of theboxes. This letter code reflects the producibility level ofcomplexity in each of the particular hole size to aspectratios. Therefore, this should be taken into account when specify-.
Note: If copper plating thickness in hole is greater than 0. These drills may be used to drillunsupported or plated-through holes in rigid printedboards.
Although the designer rarely specifies the drilled hole size,these dimensions may be used in determining minimumannular ring calculations, or minimum land sizes. Also shown in Table are the maximum board thick-nesses to which the various drill sizes should be applied. A student gets bored seeing a very long bare act. It will be tough to keep scrolling to reach page number that has Section But using index links you can just click on it and it will open Section quickly in your browser.
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