scholarly journals Design Guidelines for Anisotropic Conductive Adhesive Assemblies in Microelectronics Packaging

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Melida Chin ◽  
S. Jack Hu ◽  
James R. Barber
Keyword(s):  
Contact Resistance ◽  
Adhesion Strength ◽  
Modulus Of Elasticity ◽  
Elastic Recovery ◽  
Electrical Contact ◽  
Design Guidelines ◽  
Conductive Adhesive ◽  
Bonding Force ◽  
Anisotropic Conductive Adhesive ◽  
Number Of Particles

Multiple parameters are involved in the design of anisotropic conductive adhesive assemblies, and the overlapping influences that they have on the final electrical contact resistance represent a difficult challenge for the designers. The most important parameters include initial bonding force F, number of particles N, the adhesion strength GA, and modulus of elasticity E of the cured resin. It is well known that as the bonding force increases, the contact resistance decreases. However, when the bonding force reaches a certain maximum value, the contact between conductive particle and conductive track is disrupted due to delamination of the cured resin during the elastic recovery. The authors have shown in previous studies that the delamination is caused by high residual stresses and that it largely depends on the adhesion strength of the assembly and on the modulus of elasticity of the cured resin. Additionally, the authors have provided a methodology to quantify the maximum threshold value of the bonding force for different numbers of particles trapped between mating conductive tracks. In this paper, the relationships between contact resistance R and each one of these parameters are systematically investigated to create diagrams that give regions of robust design. Given the number of particles and their size, adhesion strength, and modulus of elasticity of the resin, the required bonding force can be found in order to achieve a desired range in contact resistance.

scholarly journals Design Guidelines for Anisotropic Conductive Adhesive Assemblies in Microelectronics Packaging

2005 ◽  
Author(s):  
M. Chin ◽  
S. J. Hu ◽  
J. R. Barber
Keyword(s):  
Contact Resistance ◽  
Adhesion Strength ◽  
Modulus Of Elasticity ◽  
Elastic Recovery ◽  
Electrical Contact ◽  
Design Guidelines ◽  
Conductive Adhesive ◽  
Electrical Contact Resistance ◽  
Bonding Force ◽  
Anisotropic Conductive Adhesive

The multiple parameters that are involved in the design of anisotropic conductive adhesive (ACA) assemblies, and the overlapping influences that they have on the final electrical contact resistance, represent a difficult challenge for the designers. The most conflicting parameters include initial bonding force F, number of particles N, adhesion strength GA, and modulus of elasticity E of the cured resin. It is well known that as the bonding force increases, the contact resistance decreases. However, when the bonding force reaches a certain maximum value, the contact between conductive particle and conductive track is disrupted due to delamination of the cured resin during the elastic recovery. The authors have shown in previous studies that the delamination is caused by high residual stresses and that it depends largely on the adhesion strength of the assembly and on the modulus of elasticity of the cured resin. Additionally, the authors have provided a methodology to quantify the maximum threshold value of the bonding force for different numbers of particles trapped between mating conductive tracks. In this paper, the relationships between contact resistance R and each one of these conflicting parameters are systematically combined to create design diagrams that give regions of robust design. It is found, for example, that for particles of radius 5μm, E = 0.9 GPa, GA = 50 J/m2, and 2 ≤ N ≤ 5, the required bonding force to achieve contact resistance within the range 7 < R < 40 mω, is 2.5 < F < 20mN.

Bulk Resistance Evaluation of Anisotropic Conductive Adhesive Particles Considering the Current Bending Effect

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
X. C. Chen ◽  
Bo Tao ◽  
Z. P. Yin
Keyword(s):  
Particle Diameter ◽  
Conductive Adhesive ◽  
Bulk Resistance ◽  
Deformation Degree ◽  
Bonding Force ◽  
Anisotropic Conductive Adhesive ◽  
Bending Effect ◽  
Current Flows ◽  
And Control ◽  
High Density Packaging

Because it is difficult to accurately estimate the electric resistance of anisotropic conductive adhesive (ACA) joints, the ACA’s applications in high density packaging field have been greatly limited. The bulk resistance of particles is an essential part of the resistance of ACA joints. For the ACA using solid nickel (Ni) particles, because current flows along the spherical profile of the particles, the bulk resistance of these particles will be underestimated if the current bending effect is neglected. Here we propose a new method, which considers this current bending effect, to accurately evaluate the bulk resistance of Ni particles. First, a mathematical model to calculate the resistance of an arbitrary shaped resistor is deduced on the basis of electromagnetic theory. Second, a numerical model is introduced to calculate the potential distribution in the particles. Finally, the bulk resistance calculated by the new model is compared with the conventional methods. It is shown that the value obtained from this model is much higher than those calculated by other methods. Furthermore, the correlation studies between the bulk resistance and the particle’s diameter, the deformation degree, and the bonding force are carried out. And the results show that these three parameters influence significantly on the bulk resistance. In conclusion, to obtain accurate bulk resistance of ACA particles and make them stable and reliable, it is important to take the current bending effect into consideration and control the particle diameter and the bonding force properly.

A Novel Anisotropic Conductive Adhesive for Lead-Free Surface Mount Electronics Packaging

2006 ◽  
Vol 129 (2) ◽  
pp. 149-156 ◽  
Author(s):  
S. Manian Ramkumar ◽  
Krishnaswami Srihari
Keyword(s):  
Magnetic Field ◽  
Contact Resistance ◽  
Surface Area ◽  
Thermal Aging ◽  
Conductive Adhesive ◽  
Lead Free ◽  
The Novel ◽  
Surface Mount ◽  
Anisotropic Conductive Adhesive ◽  
Very High

The electronics industry, in recent years, has been focusing primarily on product miniaturization and lead-free assembly. The need for product miniaturization is due to the continuous demand for portable electronic products that are multifunctional, yet smaller, faster, cheaper, and lighter. This is forcing the industry to design and assemble products with miniature passive and active devices. These devices typically have fine pitch footprints that provide a very small surface area for attachment. The solder attach technique relies primarily on the formation of intermetallics between the mating metallic surfaces. With a reduction in the surface area of the pads, the ratio of intermetallic to solder is very high once the solder joint is formed. This could result in unreliable solder joints, due to the brittle nature of intermetallics. In addition, the need to eliminate lead-based materials as a means of interconnection has renewed the industry’s interest in exploring other means of assembling surface mount devices reliably. The use of a novel anisotropic conductive adhesive (ACA) as a means for assembling surface mount devices, the ACA’s performance characteristics, and preliminary research findings are discussed in this paper. Typically, ACAs require the application of pressure during the curing process to establish the electrical connection. The novel ACA uses a magnetic field to align the particles in the Z-axis direction and eliminates the need for pressure during curing. The formation of conductive columns within the polymer matrix provides a very high insulation resistance between adjacent conductors. The novel ACA also enables mass curing of the adhesive, eliminating the need for sequential assembly. The novel ACA was found to be very effective in providing the interconnection for surface mount technology (SMT) passives and leaded, bumped, or bumpless integrated circuit packages. The requirement for precise stencil printing was eliminated, as the application of magnetic field aligned the conductive columns in the Z-axis direction eliminating any lateral conductivity. The ability to mass cure the adhesive while applying the magnetic field reduced the assembly time considerably. Placement accuracy was still found to be very critical. Shear testing of adhesive joints after thermal aging showed significance past 500 h and after temperature–humidity aging showed significance within the first 100 h. I–V characteristics of the daisy chained ball grid array devices assembled with and without bumps revealed considerable difference in the breakdown current. The correlation between initial contact resistance of the daisy chain and the final breakdown current was also determined. Preliminary experiments and findings, discussed in this paper, show the viability of the ACA for mixed SMT assembly. Further experimentations will include in situ contact resistance measurements during thermal aging, temperature–humidity aging, drop testing and thermal shock.

Effect of drop impact energy on contact resistance of anisotropic conductive adhesive film joints

2004 ◽  
Vol 19 (6) ◽  
pp. 1662-1668 ◽  
Author(s):  
Rashed Adnan Islam ◽  
Y.C. Chan ◽  
B. Ralph
Keyword(s):  
Contact Resistance ◽  
Impact Energy ◽  
Drop Impact ◽  
Conductive Adhesive ◽  
Mechanical Shock ◽  
Particle Deformation ◽  
Adhesive Film ◽  
Anisotropic Conductive Adhesive ◽  
The Impact ◽  
Microscopy Images

The contact resistances investigated in this study of anisotropic conductive adhesive film joints using Au/Ni bumps and flexible substrates are found to be increased by the drop impact energy and also by the combined effect of heat/humidity and the impact energy. The samples humidified at 85 °C/85% RH for 384 h, on which impact energy of 50 J was induced, exhibit the most severe results. The contact resistance increases by 700%, which had been about 0.062 Ω in the as-bonded condition. The samples without humidification showed a sluggish and gentle increase in contact resistance with induced drop impact energy. The contact resistance was found to be increased by 400% after absorbing 90 J energy. Scanning electron microscopy images show particle deformation due to abrasion and friction between the contacting surfaces resulting from the sudden impact. Joints are also observed with no connections, which signify open circuits. Almost 25% of circuits were found open in the samples (after 384 h in a humid environment), which have suffered severe mechanical shock. Breaking of the conductive layer of the particle and exposing the underlying polymeric portion was also observed.

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