Laminatebars - Performance History of Laminate Technology...

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Performance History of Laminate Technology
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Organic Laminate Boards
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Rigid Printed Wiring Boards (PWBs) Composite structure-organic resins reinforced with fiber Fibers are glass ( continuous filament E-glass is most often used) or other materials chosen for expansion control or cost Organic resins include epoxy,BT resin, polyimide, cyanate esters, PTFE, and phenolic Metal foil is most often used for conductors
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Classifications of Printed Wiring Boards
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Single Sided PWB’s-Starting Material Single layer of copper foil Rigid dielectric fabricated from laminating multiple layers of unclad (no copper) laminate material to the desired thickness Copper thick based on weight 1 oz/ft 2 = .00137 inches ( 1.4 mils) 2 oz/ft 2 = .00274 inches ( 2.8 mils) 1/10 oz/ft 2 = .14 mils etc.
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PWB laminate Glass is impregnated with resin. A-stage is totally uncured. Partial curing and thickness control develops B- stage material, a material that is dry to the touch but will reflow and fully cure under additional heat and pressure Final cured laminate is known as C-staged Thickness of the laminate is determined by the number of B-stage layers used. B-stage laminate is typically from 4-7 mils thick Copper foil is added and the stack is laminated
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Typical Resin Properties Material Tg E(10 6 psi) CTE (ppm) K @IMHz Epoxy 130 0.5 58 4.5 Polyimide 260 0.6 49 4.3 Cyanate Ester 260 0.5 55 3.9 PTFE 327 0.05 99 2.6 BT/epoxy 180 0.5 70 4.1
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Fiber Material Properties
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Z-Axis Expansion Due to constraining X-Y expansion due to glass/fiber mesh, Z- axis expansion is greater due to the inherent high expansion of organics( 40-600 ppm/ o C) Lower CTE fibers ( kevlar, quartz) enhance Z axis effect, although they control X-Y expansion Thermal expansion increases above T g lead to very high expansion due to the increase in CTE above T g Z-axis expansion primary cause of barrel cracking in plated- thru holes
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Z-Axis Expansion for Various Resin/Fiber Combinations
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Double sided PWBs Circuitry on both sides, with electrical access between sides provided by plated-thru-holes (PTH) Can be fabricated by subtractive or additive processes for interconnect definition Subtractive processing includes drilling, metallizing (electroless Cu), imaging,electrolytic Cu plating, and etching. Electrolytic processing requires uniform conductive coating on the board for plating Additive processing is also available and is especially important for fine line boards. Additive can start with a bare board for electroless copper plating or a thin foil to allow electroplating through a mask
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Process for a Double Sided Board Drill holes Electroless copper plate Define pattern photolithographically Electroplate copper and lead/tin solder Remove mask and etch Solder reflow ( fusing) Solder mask as appropriate Mechanical separation of individual boards
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Evolution of a Thru-hole from Drilling to Etching Drill Electroless Copper Plate Laminate Photoresist Expose and Develop Electrolytic Cu Plate Sn-Pb Plate Remove Resist Etch
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Cross-section of etching process
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