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Moisture Characteristics of Molding Compounds and Environmental Effects in PEMs Alexander Teverovsky QSS Group/Goddard Operations Alexander.A.Teverovsky.1@gsfc.nasa.gov

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11/21/02web presentation2 Moisture effects in PEMs Die level: Corrosion; Dendrites between metallization lines; Leakage current; Charge instability (lateral, ion drift, hot electron). Package level Corrosion of leads; Popcorning; Dendrite formation (on the surface and inside packages); Swelling/shrinkage: underfills in PBGA and flip-chip technology; warpage of large packages; parametric shifts in linear devices.

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11/21/02web presentation3 No humidity in space. Why moisture concerns? An obvious reason : We need to assure that no moisture related failures and no degradation occur during ground phase integration and testing period (2 to 5 years maximum). Not so obvious : We need to be aware of possible effects caused by moisture desorption in space.

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11/21/02web presentation4 Quality assurance strategy for PEMs Moisture prevention Adequate qualification testing ( do we need to use the same environmental testing as for Navy applications?) Moisture prevention strategy. Military applications: Wafer Applied Seal for PEM Protection (WASPP); Space applications: monitoring of the moisture level and baking of component and assemblies.

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11/21/02web presentation5 Purpose and Outline To discuss: Moisture diffusion characteristics of MCs: how they can be measured and used for implementation of the the moisture prevention strategy. Outline of todays presentation: Bake-out conditions for PEMs; Diffusion characteristics of MCs; In-situ technique and results of D(T) measurements.

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11/21/02web presentation6 Future presentations Do we need HAST? (Is HAST adequate to normal conditions? What are the acceleration factors? What are failure mechanisms and modes? What are possible alternatives to HAST) Environmentally induced swelling and shrinkage of molding compounds in PEMs. (Technique for swelling and shrinkage measurements; swelling characteristics of different MCs; sorption isotherms; effects of high temperature baking conditions; mechanisms of swelling and shrinkage.) Environmental hysteresis in precision voltage reference PEMs. (Effect of external mechanical stresses; effects of moisture induced swelling and bake induced shrinkage; hysteresis due to low and high temperature exposure; relaxation of parametric shifts.) Effect of moisture on characteristics, qualification testing, and reliability of chip solid tantalum capacitors.

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11/21/02web presentation7 Master curve for moisture diffusion Kinetics of water molecules concentration at the die surface and mass losses during baking of a flat package saturated with moisture. At t = C/Co=0.1, M/Mo=0.06 Bake-out time: (T) = h 2 /D(T) The first step in any MC or PEM degradation process is moisture diffusion => the characteristic times of diffusion are important for implementing the moisture prevention strategy.

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11/21/02web presentation8 Diffusion characteristics of epoxy encapsulating materials Averaged characteristics of MC: D o = 7.35 10 -6 m 2 /sec U = 0.43 eV Averaged characteristics of MC: D o = 7.35 10 -6 m 2 /sec U = 0.43 eV Data reported in literature D 85 varies ~ 10 times

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11/21/02web presentation9 Calculated moisture bake-out times for packages of different shapes and sizes

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11/21/02web presentation10 Comparison of the calculated bake-out conditions with JEDEC recommendations PackageThicknessBakeTemperature Typemm 40 C90 C125 C DIP-24 3.81996 (1608-1608) 206 (168-240) 59 (48-48) DIP-8 3.21416 (1608-1608) 146 (168-240) 41 (48-48) PQFP-44 2553 (528-1608) 57 (48-144) 16 (16-40) PLCC-32 31244 (1608-1608) 128 (168-240) 36 (48-48) TSOP-32 1138 (120-240) 14 (11-24) 4 (3-10) *Data in brackets are J-STD-033 02 recommendations

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11/21/02web presentation11 Calculated bake times at 125 o C and JEDEC recommendations Three body thickness groups per IPC/JEDEC J-STD-033A, July 2002: