TECHNICAL TIP
ADHESION ASSESSMENT AT ELEVATED TEMPERATURES
OF ELECTRICALLY CONDUCTIVE ADHESIVES
Background
The adhesion strength of an adhesive is a physical property which is temperature dependent. In most cases, the
adhesion will drop with increasing the temperature.
Overall, when exceeding the glass transition temperature (Tg) of the adhesive, the adhesion will drop significantly.
At temperatures below Tg, the material is in its rigid or “glassy” state, whereas it will be more flexible or “rubbery” at
temperatures above its Tg.
Factors such as the amount of cure, cleanliness of the parts to be bonded and the type of substrate can influence
the adhesion.
Optimum Adhesion
Typically, the longer the cure and the higher the cure temperature, the higher the adhesion. However, excessively
high cure temperatures can cause stress on the components or cracking due to rapid shrinkage. Extreme cases
can cause bubbling or even chemical degradation. It should be noted that the cure schedules on Technical
Bulletins are suggested cures. Alternative cure schedules may be more appropriate in specific applications. The
user should establish that the material meets all his requirements.
The surfaces to be bonded should be clean and degreased in order to obtain the optimum adhesion strength
possible (see also Technical Tip “Surface Preparation”).
In case of film adhesives, sufficient wetting to the surfaces of the parts to be bonded should be ensured in order to
obtain good adhesion. Applying some heat to the system reduces the resin viscosity and some pressure forces the
parts into good contact with the film. The film should be applied without trapping air bubbles between substrate
and film material (see also Technical Tip “Processing Guidelines”).
The examples below give indications of how adhesion varies with temperature for different styles of adhesive.
Page 1 of 4
TECHNICAL TIP – ADHESION ASSESSMENT AT ELEVATED TEMPERATURES
OF ELECTRICALLY CONDUCTIVE ADHESIVES
Page 2 of 4
Examples
•
Example 1 : Two Component Epoxy Adhesive : ECCOBOND 56 C / CATALYST 9 (40 / 1)
Cure : 2 h at 65°C
When subjecting parts bonded with ECCOBOND 56 C / CATALYST 9 to temperatures of 125°C, the adhesion
is higher than that obtained at room temperature. Probably the material gets a post-cure which improves
adhesion. Most likely, the Tg is exceeded at 150°C giving a lower adhesion result.
•
Example 2 : One Component Epoxy Adhesive : ABLEBOND 84-1LMI
Cure : 1 h at 150°C
Temperature of test :
Tensile Lap Shear Strength (Al/Al)
25°C
10,2 MPa
150°C
5,0 MPa
Adhesion of ABLEBOND 84-1LMI at 150°C is half of the value obtained at 25°C. Also in this case Tg (100°C)
is exceeded.
ABLEBOND 84-1LMI is widely used in the assembly of automotive and aerospace modules where the storage
and operating temperature range reaches 125°C and in some cases 150°C.
Europe
Nijverheidsstraat 7
B-2260 Westerlo
Belgium
% +(32)-(0) 14 57 56 11
Fax: +(32)-(0) 14 58 55 30
North America
46 Manning Road
Billerica, MA 01821
% 800-832-4929
% (978) 436-9700
Fax: (978) 436-9701
Asia-Pacific
100 Kaneda, Atsugi-shi
Kanagawa-ken, 243-0807
Japan
% (81) 462-258-880
Fax: (81) 462-221-347
NATIONAL STARCH MAKES NO REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, CONCERNING THE SUITABILITY OF THESE MATERIALS FOR USE IN IMPLANTATION IN THE HUMAN BODY, OR FOR ANY
OTHER USE. These materials are not designed or manufactured for use in implantation in the human body. National Starch has not performed clinical testing of these materials for implantation. National Starch has neither sought,
nor received, approval from the FDA for the use of these materials in implantation in the human body. No representative of ours has any authority to waive or change the foregoing provisions but, subject to such provisions, our
engineers are available to assist purchasers in adapting our products to their needs and to the circumstances prevailing in their business. Nothing contained herein shall be construed to imply the non-existence of any relevant
patents or to constitute a permission, inducement or recommendation to practice any invention covered by any patent, without authority from the owner of this patent. We also expect purchasers to use our products in accordance
with the guiding principles of the Chemical Manufacturers Association’s Responsible Care program.
© 2002 National Starch & Chemical Company
TECHNICAL TIP
ADHESION ASSESSMENT AT ELEVATED TEMPERATURES
OF ELECTRICALLY CONDUCTIVE ADHESIVES
•
Example 3 : Film Adhesive : ABLEFILM ECF561E and ABLEFILM 5025E
Cured at 150°C
In this particular case, the ABLEFILM 5025E develops a better adhesion strength than the ABLEFILM
ECF561E at elevated temperatures.
ABLEFILM 5025E is unsupported and has a Tg of about 90°C ; ABLEFILM ECF561E is a supported material
with a Tg of only 47°C.
Even at 250°C which is well above its Tg, ABLEFILM 5025E develops 0,38 MPa shear strength. This is double
the strength of ABLEFILM ECF561E at this temperature.
•
Example 4 : ECCOCOAT C 910-2 Silver Epoxy Dip Coating
Cured at 180°C
The data indicate that the die shear strength drops as the test temperature increases. However, ageing the
bonds for 1000 h at either 125°C or 150°C does not degrade their strength.
Page 3 of 4
TECHNICAL TIP – ADHESION ASSESSMENT AT ELEVATED TEMPERATURES
OF ELECTRICALLY CONDUCTIVE ADHESIVES
Page 4 of 4
•
Example 5 : Comparative Die Shear Strength of Various ABLEBOND Conductive Adhesives
Values are measured on 3 mm x 3 mm bare silicon die, on silver plated copper leadframe.
Adhesive
84-1LMISR4
8390
8322A
2600K
At 25°C
21,0 kg
20,0 kg
11,0 kg
8,3 kg
At 200°C
2,9 kg
2,4 kg
0,8 kg
1,0 kg
At 250°C
1,7 kg
1,2 kg
0,8 kg
0,8 kg
Notes
Rigid slow cure
Rigid snap cure
Flexible snap cure
High thermal conductivity
Conclusions
Assuming that the adhesive is fully cured, the adhesion strength drops with increasing temperature.
Although the Tg may be exceeded, some adhesion strength is maintained, and this is usually sufficient to meet the
requirements of the specific application.
16/05/2002 – TF/TW/GL
Europe
Nijverheidsstraat 7
B-2260 Westerlo
Belgium
% +(32)-(0) 14 57 56 11
Fax: +(32)-(0) 14 58 55 30
North America
46 Manning Road
Billerica, MA 01821
% 800-832-4929
% (978) 436-9700
Fax: (978) 436-9701
Asia-Pacific
100 Kaneda, Atsugi-shi
Kanagawa-ken, 243-0807
Japan
% (81) 462-258-880
Fax: (81) 462-221-347
NATIONAL STARCH MAKES NO REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, CONCERNING THE SUITABILITY OF THESE MATERIALS FOR USE IN IMPLANTATION IN THE HUMAN BODY, OR FOR ANY
OTHER USE. These materials are not designed or manufactured for use in implantation in the human body. National Starch has not performed clinical testing of these materials for implantation. National Starch has neither sought,
nor received, approval from the FDA for the use of these materials in implantation in the human body. No representative of ours has any authority to waive or change the foregoing provisions but, subject to such provisions, our
engineers are available to assist purchasers in adapting our products to their needs and to the circumstances prevailing in their business. Nothing contained herein shall be construed to imply the non-existence of any relevant
patents or to constitute a permission, inducement or recommendation to practice any invention covered by any patent, without authority from the owner of this patent. We also expect purchasers to use our products in accordance
with the guiding principles of the Chemical Manufacturers Association’s Responsible Care program.
© 2002 National Starch & Chemical Company