Test unit and enclosure for testing integrated circuits

Details Test unit and enclosure for testing integrated circuits Test unit and enclosure for testing integrated circuits

2003-09-08

2004-08-24

Ngo, Hung V. (Department: 2831)

Electricity: conductors and insulators

Anti-inductive structures

Conductor transposition

C174S051000

Reexamination Certificate

active

06781053

ABSTRACT:

FIELD
The present invention relates to integrated circuits, and more particularly, the present invention relates to testing integrated circuits.
BACKGROUND
Integrated circuits are designed to operate under a variety of environmental conditions. For example, integrated circuits are designed to operate over a range of temperatures. To ensure that an integrated circuit operates correctly over a particular range of temperatures, the integrated circuit is tested at different temperatures within the particular range of temperatures.
FIG. 1
shows a prior art test unit
101
for producing a constant temperature environment in which an integrated circuit can be tested. The test unit
101
includes a constant temperature air source
103
, a test fixture
105
, and an enclosure
107
. A die
109
, which includes an integrated circuit, is inserted in the test fixture
105
for electrical testing. The constant temperature air source
103
is capable of providing a stream of constant temperature air to the test fixture
105
. The enclosure
107
, when inserted between the test fixture
105
and the constant temperature air source
103
, provides a cavity
111
in which a constant temperature environment is created. The enclosure
107
is fabricated from stacked foam rubber pads
113
,
115
, and
117
. Each of the foam rubber pads
113
,
115
, and
117
has a hole such that when the foam rubber pads are stacked, as shown in
FIG. 1
, the holes are aligned to form the cavity
111
. Each of the foam rubber pads
113
,
115
, and
117
also has one surface
119
,
121
, and
123
, respectively, coated with a conductive material. At least one of the surfaces
119
,
121
, or
123
is attached to a ground
125
.
TABLE 1
Silicone Foam Electrostatic Discharge (ESD) Data
Free Air
Free Air
Ionized Air
Ionized Air
Decay+
Decay−
Decay+
Decay−
Coated ½″ Silicone Sheet
Grounded
0.1
0.1
0.1
0.2
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
Average
0.1
0.1
0.1
 0.12
Ungrounded
Infinite
Infinite
172.3 
207.9 
*
Infinite
Infinite
178.5 
214.1 
Infinite
Infinite
180.7 
204.5 
Infinite
Infinite
180.1 
198.3 
Infinite
Infinite
177.1 
200.3 
Average
177.74 
205.02 
Model #
Cal Date
Due Date
Ion Systems
210   
Jun. 9, 1999
Jun. 7, 2000
Charge Plate
Notes:
All tests performed with coated side of foam resting on charged plate.
All grounding done through 1 Meg. Ohm resistor to ground.
Decay test was from +/−5000 volts to +/−100 volts.
All Test Equipment Traceable to NIST.
*Non-Coated Side of silicone foam was charged to about −3K volts when first placed on charge plate.
Coated side of silicone foam was about +5 volts when first placed on charge plate ungrounded.
Table 1 shows electrostatic discharge data for a grounded sheet of silicone foam charged to ±5000 volts in free air and ionized air and an ungrounded sheet of silicone foam charged to ±5000 volts in free air and in ionized air. As can be seen from Table 1, a grounded silicone foam sheet discharges in about 100 milliseconds, and an ungrounded sheet does not discharge in free air and discharges in between about 177 seconds and about 205 seconds in ionized air.
Unfortunately, several problems can occur during the operation of the test unit
101
during the testing of the die
109
. First, an electrostatic charge
127
can accumulate on the surfaces
119
,
121
, and
123
of the enclosure
107
, and an electrostatic charge
129
can accumulate on the test fixture
105
. The accumulation of electrostatic charge
127
on the enclosure
107
and the accumulation of electrostatic charge
129
on the test fixture
105
can cause currents to flow in the test fixture
105
. The currents flowing in the test fixture
105
may damage the die
109
and any electronic circuits (not shown) connected to the test fixture
105
. The problem is particularly severe when any of the surfaces
119
,
121
, or
123
become ungrounded. As shown in the test data in Table 1, the decay time is between about 177 seconds and about 205 seconds for an ungrounded silicone sheet. This long decay time increases the likelihood of the die
109
becoming damaged by electrostatic discharge. Second, since the stacked foam rubber pads
113
,
115
, and
117
provide an enclosure having poor structural integrity, the location of the pads can change between uses of the test unit
101
. A change in pad location makes it difficult to get consistent results when performing repeatability tests using the test unit
101
.
For these and other reasons there is a need for the present invention.


REFERENCES:
patent: 4326165 (1982-04-01), Szedon
patent: 5045638 (1991-09-01), Wada et al.
patent: 5065089 (1991-11-01), Rich
patent: 5220277 (1993-06-01), Reitinger
patent: 5749178 (1998-05-01), Garmong
patent: 5838568 (1998-11-01), Dickinson et al.
patent: 5949682 (1999-09-01), Dickinson et al.
patent: 6114868 (2000-09-01), Nevill

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