Failure Analysis for ewlb-packages Strategy and Failure Mechanisms

Transcription

1 Company Logo Failure Analysis for ewlb-packages Strategy and Failure Mechanisms Florian Felux Infineon Technologies AG Neubiberg, Germany

2 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

3 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

4 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

5 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

6 ewlb schematic Image of an ewlb device 8mm x 8mm footprint of package PG-WFWLB mm x 8mm footprint) Redistribution layer Die Fan out area 6

7 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

8 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

9 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

10 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

11 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

12 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

13 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

14 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) 14

15 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

16 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

17 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 17