Technical Paper

Study of Probe Pin Internal Resistance

Prepared by Takuto Yoshida.

Presented at BiTS China Workshop, Suzhou on September 13, 2016

 

CRES Comparison by Pin Design

Pin Pitch: 0.8mm

Test Height: 2.5mm

Pin Design:

“A”: 10gf, 4‐point crimped PA

“B”: 25gf, 4‐point crimped PA

“C”: 42gf, 4‐point crimped PA

“D”: 28gf, Combined PA and Barrel

  • Higher pin force is lower CRES pin
  • Combined PA and Barrel pin (“D”) is the lowest CRES pin
  • CRES differ by pin design (18 mOhm to 33 mOhm)

CRES Composition in a Probe Pin

Note

PA: Plunger A (device side)
PB: Plunger B (PCB side)
BR: Barrel

Spring is removed from the drawing because it is no contribution to CRES path

Material Resistance

(1) PA material electrical resistance

(2) BR material electrical resistance

(3) PB material electrical resistance

Contact Resistance

(4) PA pad to PA contact resistance

(5) PA to BR contact resistance

(6) BR to PB contact resistance

(7) PB to PB pad contact resistance

Material Resistance

R: Electrical resistance (measured in ohms, Ω)

ρ: Electrical resistivity (measured in ohm⋅meters, Ω⋅m)

L: Length of material (measured in meters, m)

A: Cross-sectional area of material (measured in square meters, m2)

Total Material Resistance
R = 0.003 Ohm

  • Material resistance contribution is only 9% to 17%
  • Contact resistance is main player for pin CRES

Contact Resistance

  • R: Electrical resistance (measured in ohms, Ω)
  • Rc: Constriction resistance (measured in ohms, Ω)
  • Rf: Film resistance (measured in ohms, Ω)
  • Ro: Metal specific resistance (measured in ohms, Ω)
  • ρ: Electrical resistivity (measured in ohm⋅meters, Ω⋅m)
  • a: True contact area diameter (measured in meters, m)
  • σ: Film electrical resistivity (measured in ohm⋅meters, Ω⋅m)
  • d: Film thickness (measured in meters, m)
  • Constriction resistance contributor
    • Contact area shape
    • Contact force
    • Plating material and thickness
    • Hardness
    • Surface roughness
  • Film resistance contributor
    • Material
    • Thickness

Individual CRES Measurement

Source Meter Keithley 2400

  • Digital Multimeter Yokogawa 7555
  • PA Pad and PB Pad compress DUT
  • 3 small probes to contact DUT surface
  • R(PA Pad‐PA) = V1/0.1
  • R(PA‐BR) = V2/0.1
  • R(BR‐PB) = V3/0.1
  • R(PB‐PB Pad) = V4/0.1
  • Measure 10 times for each session with current of +0.1A and ‐0.1A by considering thermoelectric effect
  • Measured voltage was different by thermoelectric effect
  • Average voltage value for resistance calculation
New Pin Individual CRES

  • Pin Design “A” (10gf), “B” (25gf), “C” (42gf), “D” Combined PA and BR
  • Spring force is most to contact resistance of PA pad – PA, secondary for PB – PB pad
  • Combined PA and BR design for “D” design improve contact resistance of PA – BR
After 300K Cycle Individual CRES

  • Pin Design “A” (10gf), “B” (25gf), “C” (42gf), “D” (28gf) Combined PA and Barrel
  • Cycle effect mainly impact to contact resistance of BR – PB
  • Secondary impact to contact resistance of PB – PB pad
 

 

Pin Design “A” New vs. 300K

  • 300K cycle test effect mainly impact to contact resistance of BR – PB
  • Secondary impact to contact resistance of PA pad – PA
Pin Design “C” New vs. 300K

  • 300K cycle test effect mainly impact to contact resistance of PB – PB pad
  • Secondary impact to contact resistance of PA – BR
Pin Design “B” New vs. 300K vs. 3.5A 110hours

  • Current effect mainly impact to contact resistance of PB – PB pad
  • Secondary impact to contact resistance of BR – PB
  • Current effect is smaller than Pin Design “B”
  • Low temperature rise by current seems good for pin stability (Low CRES provide low heat (temperature rise))

Conclusion

  • Understand CRES Composition in a Probe Pin
  • Probe Pin CRES main player is contact resistance
  • We can measure each contact resistance by using 4‐wire measurement method
  • Higher pin force effective to reduce contact resistance of PA pad – PA
  • 300K cycle test impact to contact resistance of BR – PB (BR internal surface roughness and PB base shape seems big change)
  • 3.5A 110hours test impact to contact resistance of PB – PB pad
  • We feedback the probe pin design by result of individual CRES data