Kapton QFP Socket DC Measurement

Aries
Kapton QFP socket
DC Measurement Results
prepared by
Gert Hohenwarter
2/5/2005
GateWave Northern, Inc.
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Table of Contents
TABLE OF CONTENTS .......................................................................................................................................... 2
OBJECTIVE ......................................................................................................................................................... 3
METHODOLOGY.................................................................................................................................................. 3
Test procedures ................................................................................................................................................. 4
Setup ................................................................................................................................................................. 5
MEASUREMENTS ................................................................................................................................................. 9
Resistance ......................................................................................................................................................... 9
Current carrying capability............................................................................................................................. 10
Leakage current .............................................................................................................................................. 12
GateWave Northern, Inc.
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Objective
The objective of these measurements is to determine the DC performance of an
Aries Kapton QFP socket. Measurements are to determine parameters relevant to
test applications. Among those are current carrying ability, contact resistance and
leakage as a function of voltage.
Methodology
A four terminal (Kelvin) measurement setup is used that includes a computer
controlled voltage source capable of delivering 10 A. The voltage developed across
the contact is measured with a HP 3456A DMM and yields a V-I record.
Contact resistance testing as a function of displacement is performed in a test fixture
with a calibrated LDT linked to the data acquisition system and the same 4 terminal
measurement setup as used for the V-I-curve determination.
Leakage testing relies on acquisition of a large number of data points with
subsequent averaging to reduce noise as much as possible. In this manner, pA
leakage currents can be detected.
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Test procedures
For Cres testing the DUT plate is brought forward until electrical contact is registered.
This corresponds to a large z value. Displacement is then adjusted until the nominal
DUT position is reached. This position corresponds to z = 0.
During I-V testing drive current is increased in binary steps up to the maximum
allowable level. The dwell time for each current step is 0.5 s for V/I curves. Once the
data are available, they are processed to reveal the resistance and power dissipation
as a function of drive current.
Leakage testing is performed via computer controlled voltage source and DMM.
Voltage is increased in small steps and the associated current is recorded. From these
values, resistance is computed.
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Setup
For all tests, all contacts are grounded except for one:
Figure 1 Kapton QFP socket test arrangement; the marked pin is driven
The Kapton QFP socket is mounted on a plate as shown in Fig. 2 and tested in a
setup similar to the one shown in Fig. 4:
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Figure 2 Kapton QFP socket mounting plate example
Au over Ni plating was applied to the surfaces of the brass plate. Material type and
thickness specifications were identical to those used for PCBs.
The current/voltage probe consists of a copper post with suitably shaped surface.
This surface is Ni and Au plated. The post has two connections, thus allowing for a
four terminal measurement with very low residual resistance (about 1 milliOhm).
Figure 3 Current drive probe
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Figure 4 Test setup for 4 terminal (Kelvin) measurements
The socket with its plate is mounted in a test stand with XYZ adjustment capability:
Figure 5 Test stand
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This setup has a micrometer screw that allows repeatable adjustments in the Z
direction. Also included is a transducer that converts Z position to an electrical signal
for the data acquisition.
For resistance and current handling tests, all contacts are grounded except for one.
The socket is then placed into the test setup. A brass plunger shaped like an actual
test IC is pressed against the contacts on the DUT side of the socket. Au over Ni
plating was applied to the surface of the plunger. A four terminal (Kelvin) measurement
setup is used that included a computer controlled current source capable of delivering
10 A. The voltage developed across the contact is recorded at separate terminals with
an HP3456A digital voltmeter. Once the data are available, they are processed to
reveal the resistance and power dissipation as a function of drive current.
The same setup is used for contact resistance measurements. In this case,
connections are made only to an HP3456A DMM. It is operated in 4 wire mode for this
measurement. A precision linear potentiometer serves as a distance transducer. Its
resistance is recorded by a second HP3456A DMM.
For leakage measurements an excitation is applied to the test probe. The DUT side
of the socket is left open circuited. Leakage testing is performed via computer
controlled voltage source (10V max.) and HP 3456A DMM.
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Measurements
Resistance
The resistance as a function of deflection is an important quantity since it testifies to
the minimum compression required to achieve a valid and stable electrical connection.
It also gives a measure of placement accuracy and force application for the handler.
The observed curve for the Aries Kapton QFP socket is shown below:
Cres (z)
250
R [mOhms]
200
150
100
50
0
0
50
100
z [um]
150
GW N 504
Figure 6 Contact resistance as a function of displacement
This measurement includes the contact resistance at the pads (Cres) and the dc
resistance of the contact itself. For this graph, the value z=0 represents the maximum
compression in operation, i.e. with the DUT fully inserted. Small up/down variations in
the graph are likely the result of a ‘stop and go’ measurement because of manual
actuation of the setup.
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Current carrying capability
The measured current – voltage relationship for the Kapton QFP socket shows a
linear slope:
V and R as a function of drive current I
12
V[mV] / R [mOhms]
10
8
V
R
6
4
2
0
0
0.5
1
1.5
I [A]
2
GW N 404
Figure 7 Voltage and resistance as a function of drive current
There are no anomalies in this response.
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In lieu of a temperature measurement the power dissipation in the contact is
calculated as a function of drive current from the above measurements:
P as a function of drive current I
25
P [mW]
20
15
10
5
0
0
0.5
1
1.5
I [A]
2
GW N 404
Figure 8 Power dissipation as a function of drive current
The accompanying power dissipation in the connection never exceeds 100mW.
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Leakage current
Any conductive path between contacts can and will cause difficulties for accurate
testing of devices with high input impedances. Thus, leakage current was measured as
a function of excitation voltage between two adjacent connections:
I [pA]
Leakage current as a function of voltage
50
45
40
35
30
25
20
15
10
5
0
0
2
4
6
V
8
10
GW N 404
Figure 9 Leakage current as a function of drive voltage
Leakage is very low and is at the system limits.
When computing the corresponding resistance, very large values result:
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Resistance as a function of voltage
10000
R [GOhm]
1000
100
10
1
0
2
4
6
V
8
10
GW N 404
Figure 10 Leakage resistance as a function of drive voltage
The resistance values are at the system limits for all excitation voltages.
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