EOTPR Customer Case Studies. EUFANET Workshop: Findings OPEN?

Transcription

1 EOTPR Customer Case Studies EUFANET Workshop: Findings OPEN?

2 OUTLINE o EOTPR introduction basic scheme o EOTPR OPEN customer case studies o Open on BGA trace (evaluation) o Open on embedded BGA trace o Open at C4 bump level

3 Why use THz for a TDR system? TDR EOTPR Qualitative technique Quantitative technique 3 3

4 Terahertz Engine Schematic core of all Terahertz products Ti:Sapphire fs laser Device under test THz Emitter Probe optical fibres THz Receiver optical delay Computer 4

5 Examples of failures identified by EOTPR in 2.5D packages: Shorts, Opens, and Resistive Opens. Proven detection capability up to die. Within RDL and TSV µ-bumps (top and bottom) C4 bumps (top and bottom) Substrate trace 5

6 EOTPR fault isolation in advanced packages Position of peaks provides fault location Interposer Substrate Si Die Opens or high impedances (resistive opens) are shown by EOTPR as positive peaks EOTPR intensity (a.u.) Shorted probe Bare substrate Interposer substrate Good unit -70 Shorts or low impedances are shown by EOTPR as negative peaks BGA Package Substrate Silicon Interposer Silicon Die 6

7 TeraView EOTPR: Customer case study I Open in package substrate Device A and B both have a FIB cut in an identical trace The position of the cut is separated by ~90 µm in the devices (measured from BGA to start of the FIB cut) EOTPR can clearly identify the difference in location of the open circuit in the two devices Device A FIB cuts in traces Device B 200 BGA feature Open circuit features Failed Device A Failed Device B µm Failed Device A Failed Device B 150 EOTPR signal (a.u.) EOTPR signal (a.u.) Distance into DUT (mm) Distance into DUT (mm)

8 TeraView EOTPR: Customer case study II Open in package substrate TDR EOTPR TDR result - Fault at substrate side EOTPR result - Distance-to-Defect accurately calculated and confirmed with PFA (see next slide) 8 *Presented at IPFA 2012, paper 19-68

9 TeraView EOTPR: Customer case study II Open in package substrate PFA result: Cu trace broken at Metal7 of the substrate Design layout - Actual Distance = µm PFA result confirms EOTPR fault loaction 9 *Presented at IPFA 2012, paper 19-68

10 TeraView EOTPR customer case study III: Flip Chip An open fault was identified during electrical testing of a flip chip product. EOTPR was used to locate the fault within the failed unit. The plot below shows EOTPR waveforms from a reference bare substrate and the failed unit. The bare substrate terminates at the C4 bump pad, before the start of the C4. BGA Failed trace route C4 Contact feature Substrate termination Open in failed unit Bare substrate Failed unit

11 TeraView EOTPR customer case study III: Flip Chip The EOTPR waveforms show an open circuit in the failed unit, after the bare substrate termination. Substrate termination Open in failed unit From EOTPR we determine the fault is located 83 µm after the bare substrate termination, putting it at the die side of C4, likely at the UBM. The EOTPR fault location was subsequently confirmed by physical failure analysis as noncontact between UBM and Al contact pad. Physical failure analysis results: Good unit Failed unit C4 bump pad C4 bump 83 µm 80 µm C4 bump C4 bump pad UBM in contact with Al pad UBM not in contact with Al pad Bare substrate Failed unit

12 Comparison of EOTPR vs. conventional TDR Property EOTPR TDR EOTPR added value Input signal shape Impulse Step function EOTPR makes it easier to pinpoint faults as peak positions give fault locations. Frequency range DC to greater than 100 GHz DC to 35 GHz EOTPR higher frequency content allows for faster rise times compared to conventional TDR. Rise time < 10 ps (raw) < 6 ps (deconvolved) ~ 35 ps EOTPR faster rise time produces improved resolution compared to conventional TDR. Time base jitter < 30 femtoseconds ( seconds) > 500 femtoseconds ( seconds) EOTPR high time base stability allows for increase fault location accuracy compared to conventional TDR. Signal to noise > 64 db 45 db EOTPR high SNR increases its sensitivity to small changes in impedance

13 othanks you for your attention oquestions?

14 TeraView EOTPR: Accuracy We determine EOTPR System accuracy in the following way: Injected pulse reflects off device/interconnect Probe is displaced in 10µm steps along interconnect to demonstrate accuracy Change in position of reflected signal is measured Interconnects Probe Displacement Step size 10µm 14

15 TeraView EOTPR: Accuracy This demonstrates EOTPR has an accuracy of 30 femtoseconds. In a typical DUT this is equivalent to an accuracy of 10 µm. Reflection from end of test device track 10 repeat measurements collected at each step 0 µm 100 µm 10 µm steps 30 femtoseconds = 0.03 picoseconds = 10 µm 15

16 TeraView EOTPR: Customer case study III Package substrate impedance change EOTPR results III PFA results EOTPR signal (a.u.) I II Vendor 1 Cu trace Thinner trace Vendor 1 Vendor Distance in DUT /mm Vendor 2 Cu trace EOTPR result - show significant impedance differences between two substrate vendors. PFA result Cu trace width of vendor 1 thinner than vendor *Presented at IPFA 2012, paper 19-68