3
7303
Anisotropic Conductive Film Adhesive
Technical Data
January, 2007
Product Description
3M™ Anisotropic Conductive Film (ACF) Adhesive 7303 is a heat-bondable,
electrically conductive adhesive film. It has a slight amount of tack at room
temperature and consists of a thermosetting epoxy/acrylate adhesive matrix
randomly loaded with conductive particles. These particles allow interconnection of
circuit lines through the adhesive thickness after bonding, but are spaced far enough
apart for the product to be electrically insulating in the plane of the adhesive.
Application of heat and pressure causes the adhesive initially to flow and to bring
the circuit pads into contact by trapping the conductive particles. The thermoset
rapidly cures and provides mechanical strength. ACF 7303 may be used to bond a
flexible printed circuit to another flexible printed circuit or to a printed circuit board.
Construction
General Properties
Property
Adhesive Type
Particle Type
Particle Size
Liner Type
Adhesive Thickness
Liner Thickness
Value
Epoxy / Acrylate Blend
Silver-coated glass
43 microns
Polyester-coated Kraft with Silicone Release
74 microns
100 microns
Typical Physical
Properties and
Performance
Characteristics
Note: The following technical information and data should be considered representative
or typical only and should not be used for specification purposes.
Design Requirements
Property
Minimum Space
Between Conductors
Minimum Overlap Area
Temperature Cycling Range*
Value
250
(10)
0.75
(1200)
-40 to 80
(-40 to 177)
Units
micron
(mil)
mm
2
(mil
2
)
°C
(°F)
*Long-term outdoor use may require additional reinforcement.
3M
™
Anisotropic Conductive Film Adhesive
7303
Typical Physical
Properties and
Performance
Characteristics
(continued)
Note: The following technical information and data should be considered representative
or typical only and should not be used for specification purposes.
Ambient Physical Properties
Property
Interconnect Resistance
(1)
Insulation Resistance
Peel Strength
(1)
Modulus
(4)
(1)
(2)
(3)
(4)
Test Substrates
Flex to PC board
(2)
Flex to glass
(3)
Flex to PC board
(2)
Value
< 0.2
≥
10
10
≥
500
1 x 10
6
Units
Ohms
Ohms-cm
gf/cm
Pa
For a given application, values may differ depending on particular flex circuit and PC board materials used.
Measured for silver ink/polyester or gold coated copper/polyester flex circuits bonded to solder, tin, or gold
coated copper/FR-4 printed circuit boards. Contact overlap area was 0.75 sq. mm. Pad pitch was 500 microns.
The insulation resistance measurement was made using gold-coated copper/polyimide flex circuits bonded to
glass. Circuit line spacing was 0.19 mm. Bias voltage was 50V. Circuit line thickness was 0.058 mm.
Storage shear modulus from dynamic mechanical analysis measured at 25°C using 1 rad/sec.
Reliability Performance
Test Conditions
Notes
80°C x 1000 hrs
25°C x 4 yrs
-40°C x 1000 hrs
60°C/95% RH x 1000 hrs
70°C/95% RH x 1000 hrs
-40 to 80°C x 1000 cycles
(5)
(6)
(7)
(8)
(9)
(10)
(11)
(12)
(6-11)
(8, 12)
(8, 12)
(6, 7, 10)
(6, 7, 11)
(6, 7-11)
Interconnect Resistance
(5)
(Ω)
IPC 2.5.4
< 0.2
< 0.2
< 0.2
< 0.2
< 0.2
< 0.2
For a given application, values may differ depending on particular flex circuit and PC board materials used.
Contact overlap area was 0.75 sq. mm. Pad pitch was 500 microns.
Flex Circuit: Ag ink/PET
Flex Circuit: Au-coated Cu/PET
Flex Circuit: Au-coated Cu/PET
Flex Circuit: Au-coated Cu/PET
Flex Circuit: Au-coated Cu/PET
PC board: Sn-Pb solder-coated Cu/FR-4
PC board: Sn-Pb solder-coated Cu/FR-4
PC board: Sn-Ag-Cu solder-coated Cu/FR-4
PC board: Immersion Sn-coated Cu/FR-4
PC board: Au-coated Cu/FR-4
Contact overlap area ranged from 0.9 sq. mm to 5.4 sq. mm. Pad pitch varied from 750 microns to 2 mm.
Assembly Process
Techniques
A source of heat and pressure, such as a thermo-compression (hot bar) bonder is
required for use of 3M™ Anisotropic Conductive Film Adhesive 7303. Several
commercially available models exist; a list of vendors can be obtained by calling
the toll free number on the back of this Technical Data Sheet.
Bonding of ACF 7303 requires a three-part procedure:
• tacking the film to one circuit (pre-tacking)
• removal of the release liner
• bonding the first circuit to the second circuit.
A summary of the pre-tacking and bonding conditions is provided in the table on
page 3 and further details of the full process are given in the following sections.
-2-
3M
™
Anisotropic Conductive Film Adhesive
7303
Assembly Process
Techniques
(continued)
Assembly Conditions
Procedure
Tacking Conditions
Temperature
(13)
Pressure
Time
Bonding Conditions
Temperature
(13)
Pressure
14)
Time
(15)
(13)
Conditions
25 - 35°C
1 - 15 Bar (1 - 15 kg/cm
2
)
~1 second
140°C
>18 Bar (18.4 kg/cm
2
)
25 seconds
Temperature measured in the adhesive. Thermode set points will be higher and will depend upon the
substrate materials and bond equipment. A typical bonding set-up for a flex interconnect bond is a thermode
temperature of 200°C and a bonding time of 30 seconds (see also note 15).
Bonding pressure setting depends on the type of circuits used. Further details are provided below.
Adhesive requires approximately 25 seconds bond time after required adhesive temperature of 135-150°C
is reached to make the electrical connection. Also, it may be desirable to hold pressure while cooling for
maximum performance. Total bond time includes the time to ramp to required bond temperature (2-3
seconds), the 25 second hold at bond temperature, and cool-down time. The cool-down time will require
hold until temperature is lowered to below 90°C which is highly dependent on the type of bonder used.
(14)
(15)
Pre-tacking Method
Pre-tacking is required to attach the 3M™ Anisotropic Conductive Film Adhesive
7303 to one of the circuits to be joined. The ACF 7303 may be attached either by
hand or using automated equipment. The ACF 7303 has sufficient tack to adhere to
the surface after pre-tacking to allow the backing or liner to be easily removed. The
ACF 7303 may also be attached with automated equipment that sections the ACF
7303 to the desired length and attaches it to one of the circuits. This process may
include the application of a limited heating not to exceed 35°C. The pre-tacking
step requires a pre-tacking temperature of 25-35°C under a pressure of 1-15 Bar
(1-15 kg/cm
2
or 15-230 psi).
Release Liner Removal Method
After pre-tacking to one of the circuits, the liner must be removed. If the ACF 7303
was pre-tacked by hand the liner should be removed using a tweezers. If the ACF
7303 was attached to a printed circuit board, then a razor blade may be required to
begin to remove the liner. If the ACF 7303 was attached to flex circuitry, then the
flex can be bent slightly along the adhesive length to begin the liner removal. In
either case the liner can be fully removed using a tweezers.
If ACF 7303 is attached with automated equipment the liner removal is generally
removed by the pre-tacking equipment.
-3-
3M
™
Anisotropic Conductive Film Adhesive
7303
Assembly Process
Techniques
(continued)
Bonding Method
Final bonding must be done under heat and pressure, with a typical desirable bond
line temperature of 135-150°C, and a bonding pressure setting that depends on the
type of circuitry to be joined. For bonding flex circuitry with silver ink traces a
pressure of 18-22 bar (18.4-22.4 kg/cm
2
or 260-320 psi) should be used. An
example of the variation in contact resistance found using silver ink circuits bonded
to printed circuit boards is shown in Figure 1. A minimum in the contact resistance
was found for a bonding pressure of about 20 Bar (20.4 kg/cm
2
or 290 psi). For
bonding flex circuitry with gold/nickel/copper traces a pressure greater than 20 Bar
(20.4 kg/cm
2
or 290 psi) should be used. An example of the variation in contact
resistance found using gold/nickel/copper circuits bonded to printed circuit boards
is shown in Figure 2.
Heating the adhesive to the prescribed bonding temperature allows the adhesive to
flow and wet over the surface, and enables electrical contact to be made as the
circuit pads are pressed together. During bonding, electrical contact is typically
achieved after the bond line reaches 135-150°C. Additional time at temperature is
necessary to complete the cure of the thermoset in the adhesive. This gives the
adhesive high peel strength and reliability. The required bonding time is at least
25 seconds after the adhesive reaches the prescribed bonding temperature.
Ag-Ink-PET Test Vehicle
Contact Resistance
18
12
30
36
42
48
24
Figure 1.
Graph of relative contact resistance vs. bonding pressure using polyester flexible
printed circuitry with silver ink circuit lines bonded to printed circuit board with
gold/nickel/copper circuit lines.
0
6
Bonding Pressure (Bar)
-4-
3M
™
Anisotropic Conductive Film Adhesive
7303
Assembly Process
Techniques
(continued)
Bonding Method
(continued)
Au-Cu-PET Test Vehicle
Contact Resistance
18
12
30
36
42
48
24
Figure 2.
Graph of relative contact resistance vs. bonding pressure using polyester flexible
printed circuitry with gold/nickel/copper circuit lines bonded to printed circuit board
with gold/nickel/copper circuit lines.
A 30 second bond time, with at least 25 seconds >135°C may be used as a starting
point in developing a bond profile. Bond times may vary depending upon the
substrates to be bonded. Pressure may be released after the adhesive reaches full
cure but for maximum mechanical and electrical performance, the pressure should
be maintained while cooling to below 90°C. This increases the total bond time.
The time required to drop adhesive bond-line temperature below 90°C is highly
dependent upon the bonding equipment used.
Repair
Bonds made with 3M™ Anisotropic Condustive Film Adhesive 7303 are repairable
by heating the bond-line to above 100°C (e.g. with a hot plate or rework tool) and
peeling the circuits apart. The bond site then requires cleaning with a solvent, after
which the circuit can be re-bonded using a fresh piece of ACF 7303. Solvents such
as 3M™ Novec™ Engineered Fluid HFE-72DA or Acetone may be used.
Note: Carefully read and follow the solvent manufacturer’s precautions and
directions for use.
Storage
ACF 7303 has a shelf life of 18 months from date of manufacture when stored at
no more than 5°C (40°F) in the original, unopened package. ACF 7303 also has a
room temperature shelf life of 9 months from the converting date provided it is
stored at no more than 25°C (75°F) and is kept sealed and protected from high
humidity. ACF 7303 should be stored away from high humidity environments as
absorbed water can lead to moisture volatilization producing bubbles during heat
bonding.
-5-
0
6
Bonding Pressure (Bar)
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