6-Joyce-Board Test Workshop 2005.pdf

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Strain Limit Definition• The test is designed to define the degree ofboard flex at which point board crack initiationbegins not when the an electrical open occurs.Example of over-flexed condition. Note the board crack.12
LF Solder vs Tin-Lead Eutectic SolderComparison in Transient BendTensile force on pad1SnAgCu (LF)23LF limit5IMCs InSn matrix4PbSn limitPCB micro-strains1LFPbSnSnPb Eutectic23Pad loadbearingcapabilityTwo PhaseStructure131. The solder ball joins the substrate and thePCB by material that behaves as a spring.Lead free solder has higher stiffness thanPbSn solder, analogous to having a robustthick-wire spring coil for lead-free comparedto a thin-wire spring for PbSn solder.2. The bottom of the solder ball is attached tothe PCB. The strength of the attach point isdetermined by pad size, PCB material andconstruction, etc. The interface strength (i.e.load bearing capability for pad crater mode)between the copper pad and PCB has notchanged between PbSn and LF.3. <strong>Board</strong> bending to a given micro-strain on thePCB is tantamount to pulling apart at anoblique angle the two opposite surfaces ofthe solder ball to a given amount.4. The higher stiffness lead-free ball generateshigher forces on the pad for the same applieddeflection. The softer PbSn balls deformsmore to accommodate the applied bending,resulting in lower forces acting on the pad fora given deflection level.5. Since pad adhesion strength has notchanged, lead-free ball reaches the criticallevel of force required to pull the pad out atlower strain. This is a consequence of the ballmaterial property, not the pad property.
Page 1 and 2: Board Test Workshop 2005Board Flex
Page 3 and 4: Intro to Strain testing• As BGA p
Page 5 and 6: How do we measure strain?• We mea
Page 7 and 8: Strain Metrics• Since Strain is a
Page 9 and 10: And is less bend mode sensitive•
Page 11: Strain Limit Determination• Strai
Page 15 and 16: Intel® Board Flex InitiativeOvervi
Page 17 and 18: Mobile Components Strain LimitGuida
Page 19 and 20: Test Equipment Requirements• Data
Page 21 and 22: Gage Locations• LGA 775 socket- 2
Page 23 and 24: Demonstration• Flex test run #1
Page 25 and 26: Sample Report25
Page 27 and 28: Gage Locations27
Page 29 and 30: JEDEC 9704• Jedec Spec29
Page 31: Backup31

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