Functional capabilities of flex

1
Functional capabilities of flex
Flexelec
2
Futureproofing issues

• 42 V systems
• Digital transmission of data
• Electromagnetic compatibility

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42 V systems

• No dielectric breakdown at 20kV after 2000 hrs
  humidity testing, 2500hrs thermal cycling
• FPC layout can be designed to avoid risk of 42 V
  line to 12 V line shorting
• FPC overcurrent failure mode - adjacent tracks
  less likely to short together when insulation
  melts than with wire. Inherently safer?

4
Digital Transmission of Data

• Question Can a flexible printed circuit
  automotive harness handle the digital
  transmission of data?
• To answer this look at the physical requirements
  of a bus for an Automotive Multiplex Network

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Automotive Multiplex Networks

• Transmission of digital information between
  vehicle modules over a common bus
• Reduces the number of point to point wiring
  connections
• Standards exist to facilitate interoperability

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SAE Multiplex Network Classifications
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Controller Area Network (CAN)

• Requirements placed on physical parameters of the
  wires of the bus (ISO11898)
• Revised question can a cost effective (i.e. reel
  to reel) flexible printed circuit harness meet
  the requirements for high speed CAN?

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CAN network topology
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Electrical parameters of the bus
(ISO11898 Table 13 Physical Media Parameters of a
Pair of Wires)

• Lengthrelated resistance r
• Impedance Z
• Specific line delay

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Typical sample

• Spacing a
• Nominal 0.5 mm
• Measured 0.56 /- 0.02 mm

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Length Related Resistance

• For 35?m (1oz) copper 70 mW/m is equivalent to a
  7.6mm wide track
• A compromise width of 2mm was used for most
  samples
• This is equivalent to reducing the maximum bus
  length to 10.5m

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Impedance Results
Measured x Field solver
Acceptance region
7.6 mm tracks sample
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Specific Line Delay

• Specific line delay values less than 5ns/m
• Meets specification

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Conclusions

• Can large area FPC harnesses produced by a cost
  effective process meet the requirements of the
  ISO11898 standard?
• Yes - but
• Compromise reduced track width of 2mm implies
  reducing maximum bus length to 10.5m

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Electromagnetic Compatibility (EMC)

• Electromagnetic compatibility the ability of
  systems and equipment to function
• without adversely affecting other equipment
• being adversely affected by other equipment
• Question Is a flexible printed circuit harness
  likely to have a better or worse EMC performance
  than a wire harness?

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Why would an FPC harness have a better EMC
performance?

• In a wire harness cant control which wires lie
  adjacent in the bundle
• causes variability in performance from unit to
  unit
• In an FPC harness can control which tracks are
  adjacent
• no variability in performance?

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Why would an FPC harness have a worse EMC
performance?

• To improve EMC performance of a wire harness
  designers can use twisted wire pair or shielded
  wire
• Do structures with equivalent performance exist
  for an FPC?

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Methodology

• Compare wire and fpc structures in standard EMC
  tests

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Automotive Component Tests
SAE J1113-25 Tri-plate line
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Cable Tester
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Samples - wire

• Worst caseSingle unscreened wire - return
  through earth
• Best caseBMW twisted wire pair, 74?360?
  twists per meter

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Samples - FPC

• Coplanar twin track
• Through hole twisted pair (10 repeats/m)

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Samples - FPC

• Twisted pair emulator (wiggly track, 139
  repeats/m)

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Samples - FPC

• Shielded coplanar track

No shielding here
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Results 1-30 MHz
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Results 20 MHz to 1 GHz
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Results 1-30 MHz
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Results 1-30 MHz
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Ranking of samples
WORST

• Single wire earth return
• Coplanar twin tracks
• Twisted pair emulator
• Twisted wire pair/through hole FPC
• Shielded coplanar twin tracks

BEST
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Conclusions

• All FPC structures perform better than a single
  wire with earth return over the 1-30MHz range
• The coplanar tracks and twisted pair emulator are
  particularly cost effective methods of gaining
  improvement in EMC performance