Scanning Acoustic Microscopy usually used for detection of delamination extended for new applications: ⢠Detection of delaminated balls. ⢠Detection of cracks.
Failure Analysis for eWLB-Packages Strategy and Failure Mechanisms Florian Felux Infineon Technologies AG Neubiberg, Germany
Purpose • Demonstration of adaption and application of various analysis methods for eWLB packages • Distinction of die and package related failures • Front side- or back side- analysis approach • Methods for top down- and cross section preparation • Application shown for two case studies 2
Outline • eWLB: New package technology by Infineon • Schematic concept of extendedWaferLevelBGA • Failure Analysis capabilities for eWLB devices • Challenges in reconditioning of devices for testing and analysis • Capabilities of scanning acoustic microscopy • Localization techniques from both die sides • Top down reverse engineering • Mechanical cross section preparation • Two case studies • Summary 3
eWLB: New package by Infineon • New package introduced by Infineon in 2009 • Smaller and thinner package compared to F2BGA • New package challenges failure analysis • Capabilities of 3D integration
Asic1 Asic2 4
eWLB schematic • extended Wafer Level Ball grid array • Backend-process in parallel for multiple dies on wafer-level • Layer by layer process right upon die resulting in packaged components on artificial wafer • Dielectric 1 on die act for stress relief • Cu RDL redistributing terminals from die to solder ball positions • Dielectric 2 protecting Cu RDL Fan-Out area (mould)
Si-Die
Dielectrics 1 and 2
ReDistribution Layer (RDL)
Solder Ball 5
eWLB schematic • Image of an eWLB device • 8mm x 8mm footprint of package PG-WFWLB-217-1
8mm x 8mm footprint)
Redistribution layer
Die
Fan out area 6
Challenges for reconditioning eWLB for testing and analysis • Customer returns need to be reconditioned before testing and analysis can be performed • This turned out to be more challenging than expected…
Solder bridges on reconditioned component
Damaged silicon under lifted ball 7
Challenges for reconditioning eWLB for testing and analysis • Cu ball pad necessary to form alloy with solderball • If Cu ballpad entirely used up, no alloy formation possible -> Reconditioned ball will not stick
“Missing ball” after reconditioning Before being able to perform analysis on eWLB, reconditioning processes needed to be specifically developed 8
Capabilities of scanning acoustic microscopy Scanning Acoustic Microscopy usually used for detection of delamination extended for new applications: • Detection of delaminated balls • Detection of cracks by thinning of component and scanning through die at 300MHz
9
Capabilities of scanning acoustic microscopy
RDL In place but delaminated solder ball (75 MHz)
Cracks under balls at mechanically overstressed components (300MHz)
For the inspection of material interfaces and their integrity SAM is well qualified 10
Localization techniques from both sides Backside
Frontside
Localization tool (e.g. TIVA, EMMI, Thermography)
Localization tool (e.g. Thermography))
Socket Contact via special socket
Contact via microprobes
eWLB is well suitable for backside localization while maintaining full electrical functionality 11
Top down reverse engineering Solder ball etch with organic acid while all other metals/ dielectrics are protected.
Right after solderball etch: Scanning Electron Microscopy (SEM) image of formation of intermetallic compounds
12
Top down reverse engineering Selectively de-processing of the redistribution layer and dielectrics using wet- and dry- chemistry
Component after ball pad removal Cu lines and dielectrics are still present
Specific selective etch recipes developed in FA for each layer of the eWLB stack
13
Mechanical cross section preparation Embedded mechanical cross sections to analyze dedicated locations of the eWLB package or die • Transparent polymer for embedding • Excellent optical control of grinding progress with high precision because eWLB dielectrics are mostly transparent
Top down image of an embedded component during grinding Check exact position of cross section quite easy (black arrows) (Grinding surface acts as a mirror)
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Case study 1 • Die wet chemically prepared to expose area under ball while dielectric remained on all other areas revealed crack • SEM image of die with cracks after complete eWLB package removal
• Mechanical cross section through crack showed crack propagation
Dielectric 1 Top metal 15
Case study 2 • Short localized by Thermally Induced Voltage Alteration (TIVA) under RDL contact pad • Solder ball pad chemically removed • Visual inspection of TIVA localized area showed meltdown in contact pad area • SEM image of local meltdown at top metal lines
Imide Ball edge
Via in ball pad 16
Summary • Reconditioning is more challenging than expected • Mechanically induced cracks are well detectable using high frequency ultrasonic microscopy • eWLB well suitable for backside localization “by design“ • All backside localization techniques are easily applicable • Top down reverse engineering is possible with high selectivity
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