Functionality Test of Bare Modules for the Phase I Upgrade of CMS Pixel Detector Presentation of Master Thesis, 23.10.2015 Bojan Hiti INSTITUT F ¨ UR EXPERIMENTELLE KERNPHYSIK (EKP), KIT www.kit.edu KIT – University of the State of Baden-Wuerttemberg and National Laboratory of the Helmholtz Association
Outline Motivation for the Phase I Upgrade Structure of pixel modules and bump bonding technology Bare module production at KIT and motivation for the functionality test Bare module probe station setup Test routines on bare modules Evaluation of test reliability Production yields and conclusion Bojan Hiti – Functionality Test of Bare Modules for the Phase I Upgrade of CMS Pixel Detector October 23, 2015 2/17
CMS Pixel Phase I Upgrade LHC Run 2: 13 TeV center of mass energy for pp 2 × 10 34 cm − 2 s − 1 instantaneous luminosity (doubled design luminosity) Increased luminosity challenging for the CMS pixel detector Particle rate up to 600 MHz cm − 2 (Run 1: 115 MHz cm − 2 ) Significant data loss with the current pixel detector due to buffer overflows (up to 50 % data loss in the innermost layer) For this reason a new pixel detector will be installed in CMS during the Phase I Upgrade (2016/2017) and will be used until Phase II Bojan Hiti – Functionality Test of Bare Modules for the Phase I Upgrade of CMS Pixel Detector October 23, 2015 3/17
CMS Pixel Phase I Upgrade Detector changes in the Phase I Upgrade: New readout chip (ROC) Additional layer 4 Layer 1 closer to the interaction point → reduced beam pipe diameter Power supplies moved outside of the active volume Institutes involved in Phase I: PSI (CH), CERN, INFN (I), DESY (D), KIT & RWTH Aachen (D) KIT will produce one half of the modules required for barrel layer 4 Bojan Hiti – Functionality Test of Bare Modules for the Phase I Upgrade of CMS Pixel Detector October 23, 2015 4/17
CMS Pixel Detector Module Smallest building block of the pixel detector 350 modules for Phase-I-Upgrade will be produced at KIT (4/day) Bojan Hiti – Functionality Test of Bare Modules for the Phase I Upgrade of CMS Pixel Detector October 23, 2015 5/17
CMS Pixel Detector Module Smallest building block of the pixel detector 350 modules for Phase-I-Upgrade will be produced at KIT (4/day) Intermediate step in module assembly: Bare module: Sensor and 16 ROCs Bojan Hiti – Functionality Test of Bare Modules for the Phase I Upgrade of CMS Pixel Detector October 23, 2015 5/17
Bump Bonding Hybrid detector design: sensor and ROCs manufactured on separate chips Electrical interconnections on pixel level required → bump-bonding (BB) Bump-bonding: vertical interconnections via solder balls (size ∼ 30 µ m ) 4160 solder bumps per ROC 66 560 bumps per module 99 % good BB connections per ROC for class A module required Bare Module: REWORK of defect ROCs still possible Early discovery of bonding issues Bojan Hiti – Functionality Test of Bare Modules for the Phase I Upgrade of CMS Pixel Detector October 23, 2015 6/17
Bare Module Production at KIT Process taking place in a class ISO 10000 clean room Bojan Hiti – Functionality Test of Bare Modules for the Phase I Upgrade of CMS Pixel Detector October 23, 2015 7/17
Bare Module Production at KIT Process taking place in a class ISO 10000 clean room Process steps: Cleaning of electrical components Bojan Hiti – Functionality Test of Bare Modules for the Phase I Upgrade of CMS Pixel Detector October 23, 2015 7/17
Bare Module Production at KIT Process taking place in a class ISO 10000 clean room Process steps: Cleaning of electrical components Optical inspection of sensors and bumped ROCs Bojan Hiti – Functionality Test of Bare Modules for the Phase I Upgrade of CMS Pixel Detector October 23, 2015 7/17
Bare Module Production at KIT Process taking place in a class ISO 10000 clean room Process steps: Cleaning of electrical components Optical inspection of sensors and bumped ROCs Flip-chip bonding Bojan Hiti – Functionality Test of Bare Modules for the Phase I Upgrade of CMS Pixel Detector October 23, 2015 7/17
Bare Module Production at KIT Process taking place in a class ISO 10000 clean room Process steps: Cleaning of electrical components Optical inspection of sensors and bumped ROCs Flip-chip bonding Bare module test Eventual reworking Bojan Hiti – Functionality Test of Bare Modules for the Phase I Upgrade of CMS Pixel Detector October 23, 2015 7/17
Bare Module Production at KIT Process taking place in a class ISO 10000 clean room Process steps: Cleaning of electrical components Optical inspection of sensors and bumped ROCs Flip-chip bonding Bare module test Eventual reworking Reflow soldering Bojan Hiti – Functionality Test of Bare Modules for the Phase I Upgrade of CMS Pixel Detector October 23, 2015 7/17
Bare Module Production at KIT Process taking place in a class ISO 10000 clean room Process steps: Cleaning of electrical components Optical inspection of sensors and bumped ROCs Flip-chip bonding Bare module test Eventual reworking Reflow soldering Bojan Hiti – Functionality Test of Bare Modules for the Phase I Upgrade of CMS Pixel Detector October 23, 2015 7/17
Principles of the Bare Module Test Electrical test of bare modules based on injection of internal calibration signals in the ROC During the test, a temporary electrical connection to wire-bond pads on the ROC needed (wire-bond pads remain intact): Needle Card Custom readout board (DTB) – ROC powering and readout via needle card connection Additionally: − 150 V bias voltage applied → bias needle Bojan Hiti – Functionality Test of Bare Modules for the Phase I Upgrade of CMS Pixel Detector October 23, 2015 8/17
Bare Module Probe Station Setup Bojan Hiti – Functionality Test of Bare Modules for the Phase I Upgrade of CMS Pixel Detector October 23, 2015 9/17
Bare Module Probe Station Setup Probe station for the electrical test of bare modules built from scratch NI LabWindows based control software (GUI) Pixel eXpert Analysis Readout (pXar) – software for running electrical tests Driving to test positions and execution of electrical test automated Module positioning via pattern recognition Operator input required for the confirmation of steps and evaluation of results Bojan Hiti – Functionality Test of Bare Modules for the Phase I Upgrade of CMS Pixel Detector October 23, 2015 10/17
Electrical Test Tests conducted on a bare module: I-V curve – discover sensors with increased leakage current Pretest – set ROC currents and configure internal calibration signals Pixel alive – discover dead pixel unit cells Bump bond test - find missing bump bonds Bare modules classified in three quality classes: A (best), B and C (worst), depending on the test outcome Compared to other production centers, KIT bumps have larger size → Direct application of the standard bump bond test not reliable → A custom bump bond test had to be developed → Another bump bond developed in parallel at DESY, used at KIT for cross checking Bojan Hiti – Functionality Test of Bare Modules for the Phase I Upgrade of CMS Pixel Detector October 23, 2015 11/17
Electrical Test Pixel Alive: check responsiveness of pixel unit cells 10 calibration signals injected directly into the preamplifier Pixels with no hits identified as dead PixelAlive PixelAlive 80 10 row hits 9 N 8 60 7 6 40 5 4 3 20 2 1 0 0 0 10 20 30 40 50 column Bojan Hiti – Functionality Test of Bare Modules for the Phase I Upgrade of CMS Pixel Detector October 23, 2015 12/17
Electrical Test Pixel Alive: check responsiveness of pixel unit cells BB-test step 1: Set optimal amplifier threshold on ROC level Run a noise scan (no signal injection) Vary threshold level and count noisy pixels Minimal threshold with less than 5 noisy pixels selected noisy pixels Low threshold 10 3 10 2 0 noisy pixels selected 8 noisy pixels threshold 10 100 105 110 115 120 125 130 vthrcomp Bojan Hiti – Functionality Test of Bare Modules for the Phase I Upgrade of CMS Pixel Detector October 23, 2015 12/17
Electrical Test Pixel Alive: check responsiveness of pixel unit cells BB-test step 1: Set optimal amplifier threshold on ROC level BB-test step 2: 100 calibration signals injected via air gap capacitance into the sensor and collected through the bump-bond Measure pixel efficiency – fraction of received triggers (cut 50 % ) Efficiency Map CalDel = 150 Efficiency Map CalDel = 150 80 100 Efficiency [%] row 90 80 60 70 60 40 50 40 30 20 20 10 0 0 0 10 20 30 40 50 column Bojan Hiti – Functionality Test of Bare Modules for the Phase I Upgrade of CMS Pixel Detector October 23, 2015 12/17
Test Duration 5 min Insert Module + Alignment I-V curve 5 min Test 16 ROCs - drive to ROC 16 × 4 min - pretest, pixelalive - bump-bonding test Also ROCs with a weak 5 min per ROC or more Manually test ”bad” ROCs needle contact, which have to be retested 5 min Fill database entries Bojan Hiti – Functionality Test of Bare Modules for the Phase I Upgrade of CMS Pixel Detector October 23, 2015 13/17
Comparison with X-ray Measurements X-ray test: independent verification of the bump bond test Signals generated by full absorption of X-ray photons Only possible on a fully built module (no more reworking) Bojan Hiti – Functionality Test of Bare Modules for the Phase I Upgrade of CMS Pixel Detector October 23, 2015 14/17
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