ESA s approach to quality control of the supply chain for PCBs. Stan Heltzel European Space Agency

Transcription

1 ESA s approach to quality control of the supply chain for PCBs Stan Heltzel European Space Agency

2 Outline A. ESA s approach to supply chain control for PCBs B. Case study: contamination in PCBs 1. Problem description 2. Risk mitigations 2

3 ESA Projects: NRB, RFx, reviews Qualification: Test, Audit, NCR ECSS: Standardisation PCB/SMT WG: Harmonisation R&D PCB manufacturer Procurement: DR + MRR, Test, NCR Equipment manufacturer 3

4 ECSS European Cooperation for Space Standardisation ECSS-Q-ST-70-10C PCB qualifcation (revision ongoing) ECSS-Q-ST-70-11C PCB procurement (revision ongoing) ECSS-Q-ST-70-12C PCB design (first issued July 2014) In addition, Process Identification Documents (PID) describe qualified technology domain of each PCB manufatcurer. 4

5 Harmonisation of electronic technologies ECSS standardisation ecss.nl PCB/SMT WG with industry in the Component Technology Board technology roadmaps escies.org, spacecomponents.org 5

6 Technology drivers PCB are platform for placement and routing for complex components PCB Area Array Device ~2 keuro ~20 keuro PCBs need to be comparable to components in terms of reliability and complexity, but for a much lower cost. High pint count causes complex routing Miniaturization requires dense routing Signal integrity requires short routing 6

7 Reliability issues PCB material selection driven by assembly and repair, not by space environment PCB build-up driven by capability and miniaturization, not by manufacturability Material, build-up and metallisation processes affect reliability of interconnections Design and manufacturability are key 7

8 Qualification - Request for qualification: support, market, ESA projects - Qualification ECSS-Q-ST Audit - Qualified domain published in PID and on escies.org/pcb/ - Design & Procurement by OEMs - Periodic audit and re-qualification 8

9 ESA Projects: NRB, RFx, reviews Qualification: Test, Audit, NCR ECSS: Standardisation PCB/SMT WG: Harmonisation R&D PCB manufacturer Procurement: DR + MRR, Test, NCR Equipment manufacturer 9

10 B. Case study: contamination - Outline 1. Problem description a. Latent short circuit failure b. Failure mechanism c. Contamination d. IR testing 2. Risk mitigations a. Design b. Manufacture c. Base material supply 10

11 1. Latent short circuit - Introduction Short circuit failure occurred in PCBs for power distribution after prolonged functional testing in ambient lab environment or after thermal vacuum cycles. 11

12 1. Latent short circuit - Failure Mechanism Electromigration caused by: Pathway Electrolyte Bias voltage Dendritic growth (SIR) Conductive Anodic Filament 12

13 1. Latent short circuit - Pathway Resin-glass interface Hollow glass fibers Congolmerated flame retardant or fillers Delamination Voids Cracks [EA-2010-MAT-12B] Contamination by foreign material 13

14 1. Latent short circuit - Contamination Sources: PCB manufacturing processes Base material supply Types: Cl-bearing particles Metallic debris Organic residue Dust Fibers FR4 resin dust in polyimide etc 14

15 1. Latent short circuit IR test sistance_dieelectric_materials_ipc.pdf fiber contaminated no contamination observed T0 after 200TC after 500TC T0 after 200TC after 500TC 15

16 1. Latent short circuit IR test conclusions Fiber contamination provides pathway for electromigration 16

17 2. Risk mitigation PCB design IPC-2221 ECSS-Q-ST Space product assurance PCB design Example: 4 mil laminate with 2 oz Cu can have a min projected peak-to-peak dielectric thickness of 68 µm. Take account of tolerances in dielectric thickness Take account of etching tolerances for in-plane clearances Margin for double insulation of critical signals Presence of non-functional pads 2 sheets of glass reinforcement between copper layers 17

18 2. Risk mitigation PCB manufacturer a) Incoming sample inspection on base laminate 18

19 2. Risk mitigation PCB manufacturer b) Inspection on etched inner layers: 100% visual inspection on light table 19

20 2. Risk mitigation PCB manufacturer b) Inspection on etched inner layers: AOI 20

21 2. Risk mitigation PCB manufacturer c) Cleanliness control plan QT/2013/730/SH Recommendations: Cleanliness control between Cu oxidation and lay-up Restrictions on the use of materials that show static charging Class cleanroom in lay-up area Class cleanroom on flow bench De-ionisation equipment at lay-up 21

22 2. Risk mitigation PCB manufacturer d) Cleaning and inspection of ecthed inner layers and prepreg Clean tacky roller vacuum hovering Inspect UV fluorescence bright light 22

23 2. Risk mitigation PCB manufacturer e) Inspection on external layers Note: these are laminates, not prepreg 23

24 2. Risk mitigation PCB manufacturer f) High resistance electrical testing IPC-9252 IPC6012 class 3/a QT/2013/681/SH 10 V 250 V 250 V 10 MΩ 100 MΩ 1 GΩ V drop during ramp up is a failure Direct resistive testing 1.27 mm adjacency 24

25 2. Risk mitigation IPC-4101 base laminate Test frequency Pass/fail criteria Consequences of failure 25

26 2. Risk mitigation IPC-4101 base laminate Proposal for cleaner class of base materials [QT/2013/378/SH] Prepreg delivered as b-stage cured sheets Prepreg for manufacture of laminate Increase inspection frequency to 100% Laminate Reduce permittable fibre length from 13 mm to 0.5 mm Increase sample frequency to 2% Reject entire lot if test is non-compliant 26

27 Conclusions Interactions in supply chain identified contamination problems. Risk mitigations specified in design, manufacture and base material supply. New procurement specification in use and proposed to IPC

28 Thank you for your attention!