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
- 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
- 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
- 300K cycle test effect mainly impact to contact resistance of BR – PB
- Secondary impact to contact resistance of PA pad – PA
- 300K cycle test effect mainly impact to contact resistance of PB – PB pad
- Secondary impact to contact resistance of PA – BR
- 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))
