Center Probe BGA 0.8mm Socket Electrical

Giga Test Labs
POST OFFICE BOX 1927 CUPERTINO, CA
95015
TELEPHONE (408) 524-2700 FAX (408) 524-2777
ARIES ELECTRONICS
BGA SOCKET
(0.80MM TEST CENTER PROBE CONTACT)
Final Report
Electrical Characterization
0.05-5.05 GHz
Feburary 21, 2003
1
Table of Contents
Subject
page
Table of Contents..................................................................................................2
Summary...............................................................................................................3
Objective..........................................................................................................3
Methodology: ...................................................................................................3
Figure 1: Surrogate Package......................................................................3
Figure 2 – Socket Fixture ...........................................................................4
Figure 3 – Signal pin load conditions..........................................................4
Measurement system ......................................................................................5
Equivalent-circuit model...................................................................................5
Figure 4 - BGA socket equivalent-circuit diagram ......................................5
Element definitions ..........................................................................................6
Element values ................................................................................................6
Table 1 – BGA socket (0.80mm Test Center Probe Contact) element
values .........................................................................................................6
Conclusions .....................................................................................................6
Table 2 – BGA socket (0.80mm Test Center Probe Contact) 1dB loop-thru
bandwidth ...................................................................................................6
Figure 5 – Signal to ground ratio setup ......................................................7
Appendix ...............................................................................................................8
2
Summary
Objective
The Aries BGA (0.80mm Test Center Probe Contact) socket was measured at
GigaTest Labs to assess its electrical performance. Also, its high-speed
performance limits were determined.
Methodology:
A custom fixture (GTL 243-GT-001 rev A1) was first designed by GTL which
allows the use of coplanar probes to make the measurements. A second fixture
was fabricated to be placed inside each socket. It provides connections between
the internal pins, so pairs of pins can be measured in different load conditions.
This fixture is referred to as "surrogate package". Figure 1 shows a picture the
surrogate package, while figure 2 shows the top and bottom side of the fixture.
Figure 1: Surrogate Package
3
Figure 2 – Socket Fixture
There are three load conditions used on the signal pins: the open measurement
is performed on two pins with just unconnected surface pads on the surrogate
package. The short measurement is done with the pins shorted to the ground
on the surrogate. The thru is just the two pins connected together. These are
illustrated on figure 3. The measured pins are denoted by the numbers 1 & 2.
The adjacent pins to the measurement, usually the three nearest neighbors are
grounded to the fixture ground and the surrogate package ground.
open
short
thru
1
1
1
2
2
2
Figure 3 – Signal pin load conditions
The fixture was measured separately to extract its parasitics, so they could later
be de-embedded from the overall measurement.
The Agilent 8510C network-analyzer was used to measure two-port sparameters. The frequency range was 100 MHz – 40.1 GHz. From the sparameter data, a SPICE-compatible equivalent circuit was derived using Agilent
ADS version 2002.
4
Measurement system
All measurements were taken using a high-frequency measurement system.
This consists of a Agilent 8510C network analyzer & GGB Picoprobes™ 450 µm
pitch. The Agilent 8510C network analyzer is a frequency domain instrument.
The measurements are taken as scattering parameters (a.k.a. s-parameters).
The HP8510C has great calibration capabilities, which make it the most accurate
high-frequency instrument available. For this work the short-open-load-thru
(SOLT) calibration was used. The GGB Picoprobes provide a high-quality 50 Ω
path from the network analyzer and cables to the DUT.
Equivalent-circuit model
Figure 4 shows the topology used to model the BGA socket (0.80mm
Test Center Probe Contact). Please note that only two pins are shown
in this schematic, however there will be similar mutual elements (M21, C21A and
C21B) to ALL the surrounding pins. Therefore, to implement the model for one
pin, the user needs to describe it and all the pins surrounding it (a total of 9 pins).
By the same reasoning, to implement two pins, then the models for 12 pins will
be needed.
C21b
R1
L1
M21
L2
R2
C21a
port 1
port 2
Figure 4 - BGA socket equivalent-circuit diagram
5
Element definitions
L1, L2:
pin effective inductance
M21:
mutual inductance between adjacent pins
R1, R2:
shunt-resistance of inductors L1 and L2, used to model highfrequency loss due to skin effect and dielectric loss
C21a:
mutual-capacitance between adjacent pins (PCB side)
C21b:
mutual-capacitance between adjacent pins (BGA side)
Element values
The BGA socket (0.80mm Test Center Probe Contact) model is
valid from DC to 5.05 GHz. The measured and modeled transmission response
agrees within 1 dB. Models were extracted for four types of pins: adjacent field
pins, corner pins, field diagonal pins and edge adjacent pins.
Table 1 – BGA socket (0.80mm Test Center Probe Contact) element values
Pins
L1 & L2
(nH)
M21
(nH)
R1 & R2
(Ω)
C21a
(pF)
C21b
(pF)
Field adjacent
0.56
0.08
200
0.033
0.033
Corner adjacent
0.76
0.17
300
0.043
0.043
Field diagonal
0.51
0.01
300
0.007
0.007
Edge adjacent
0.65
0.12
200
0.040
0.040
Conclusions
1. The bandwidth for the BGA socket (0.80mm Test Center
Probe Contact) was determined from a loop-thru measurement on two
adjacent pins with varying numbers of surrounging pins grounded (please see
figure 5 and table 2).
Table 2 – BGA socket (0.80mm Test Center Probe Contact) 1dB loop-thru
bandwidth
Pins
1dB BW
(GHz)
Field adjacent (1:5 signal to gnd ratio)
7.8
Corner adjacent (1:2 signal to gnd ratio)
7.1
Field diagonal (1:7 signal to gnd ratio)
10.1
Edge adjacent (1:3 signal to gnd ratio)
8.5
6
1:2
1:3
1:5
probed pin
grounded pin
1:7
Figure 5 – Signal to ground ratio setup
Since the surrogate packages were routed out to fit into the socket cavity, we
believe there was a small misalignment on the field adjacent THRU standard.
This issue is probably responsible for the low field adjacent bandwidth. We
attempted this measurement twice, with no better result. In reality, the field
adjacent 1 dB bandwidth should be in the 9-10 GHz range.
2. The model bandwidth is DC-5.05 GHz, which will easily handle signals with
200 ps edges.
7
Appendix
The appendix shows the measured and simulated output data.
Measured and simulated data
page
Open measurement on adjacent pins ...................................................................9
Shorted measurement on adjacent pins .............................................................10
Loop-thru measurement on adjacent pins...........................................................11
Loop-thru bandwidth measurement (40 GHz) ............................................... 12-15
8
Adjacent pins open
Measured s-parameters in blue, simulated s-parameters in red
9
Adjacent pins shorted to ground
Measured s-parameters in blue, simulated s-parameters in red
10
Adjacent pins connected together (loop-thru)
Measured s-parameters in blue, simulated s-parameters in red
11
Adjacent Loop-thru Bandwidth Measurement
Measured insertion loss versus frequency for two pins in series
“1:5 signal to ground ratio”
L o o p -Thru Bandw idth
0
m1
dB(S(2,1))
-1
-2
m1
fre q = 7 . 8 0 0 G H z
d B (S(2,1))=-0.978
-3
-4
-5
0
5
10
fre q , GHz
12
15
20
Edge Loop-thru Bandwidth Measurement
Measured insertion loss versus frequency for two pins in series
“1:3 signal to ground ratio”
L o o p -Thru Bandw idth
0
m1
dB(S(2,1))
-1
-2
m1
fre q = 8 . 5 0 0 G H z
d B (S(2,1))=-0.960
-3
-4
-5
0
5
10
fre q , GHz
13
15
20
Corner Loop-thru Bandwidth Measurement
Measured insertion loss versus frequency for two pins in series
“1:2 signal to ground ratio”
L o o p -Th r u B a n d w idth
0
m1
dB(S(2,1))
-1
m1
fre q = 7 .1 0 0 G H z
d B (S(2,1))=-0.918
-2
-3
-4
-5
0
5
10
fre q , GHz
14
15
20
Diagonal Loop-thru Bandwidth Measurement
Measured insertion loss versus frequency for two pins in series
“1:7 signal to ground ratio”
L o o p -Thru Bandw idth
0
m1
dB(S(2,1))
-1
-2
m1
fre q = 1 0 .10GHz
d B (S(2,1))=-0.971
-3
-4
-5
0
5
10
fre q , GHz
15
15
20