(Anisotropic conductive adhesive film)
Anisotropic Conductive Film (ACF).
Anisotropic Conductive Film
As electronics become lighter and thinner
Anisotropic conductive adhesive film (A
Mainly include resin adhesive
table of Contents
00001. 1 Preface
00002. 2 conductive adhesive film
00003. 3 brands and differences
00004. 4 reliability requirements
With the rapid development of electronic products toward lightness, thinness, shortness, and miniaturization, almost all kinds of portable electronic products use liquid crystal displays as display panels, especially in camcorders, notebook computers, mobile terminals or personal digital processing. LCD and other products, LCD has become an important component. In addition to the liquid crystal panel of the liquid crystal display, a driving chip must be linked to the periphery of the liquid crystal display to control the display signal. Generally speaking, the interface connection technology between the LCD panel and the driver IC system can be roughly divided into the following types: Tape Automated Bonding (TAB), Chip on Glass; COG), Chip-Flex (COF).
ACF conductive adhesive film
Anisotropic Conductive Film (ACF)
2.1 What is an anisotropic conductive adhesive: It is characterized by a significant difference in electrical resistance between the Z-axis electrical conduction direction and the XY insulation plane. When the difference between the Z-axis on-resistance value and the XY plane insulation resistance value exceeds a certain ratio, it can be called a good conductive anisotropy.
2.2 Continuity principle: The electrodes between the IC chip and the substrate are connected with conductive particles to make them conductive, and at the same time, the short circuit between the two adjacent electrodes can be avoided, and the purpose of conducting only in the Z-axis direction is achieved.
2.3 Product classification: 1. Anisotropic conductive paste. 2. Anisotropic conductive film . Anisotropic conductive film (ACF) has the characteristics of continuous processing (Tape-on-Reel) with very low material loss, so it has become a more commonly used product form.
2.4 Main composition: It mainly includes resin adhesive and conductive particles. The function of the resin adhesive is to prevent moisture, then heat resistance and insulation. It mainly fixes the relative position of the electrode between the IC chip and the substrate, and provides a pressing force to maintain the contact area between the electrode and the conductive particles.
General resins are divided into two categories: thermoplastic resins and thermosetting resins. Thermoplastic materials mainly have the advantages of low temperature adhesion, fast assembly, and easy rework, but they also have the disadvantages of high thermal expansion and high hygroscopicity, which makes them easy to degrade at high temperatures and cannot meet the requirements of reliability and reliability. Thermosetting resins such as epoxy and polyimide have the advantages of high temperature stability, low thermal expansion and low hygroscopicity, but the disadvantages of high processing temperature and the difficulty of reworking, but the advantages of high reliability are still present. Uses the widest range of materials.
In terms of conductive particles, the anisotropic conductive properties mainly depend on the filling rate of the conductive particles. Although the conductivity of anisotropic conductive adhesive will increase as the filling rate of conductive particles increases, it will also increase the probability of short circuits caused by contact between conductive particles.
In addition, the particle size distribution and distribution uniformity of the conductive particles will also affect the anisotropic conductive properties. Generally, conductive particles must have good particle size uniformity and roundness to ensure that the contact area between the electrode and conductive particles is consistent, maintain the same on-resistance, and at the same time avoid that some electrodes are not in contact with the conductive particles, resulting in an open circuit. The situation happened. The common particle size range is 3 ~ 5μm. Too large conductive particles will reduce the number of particles contacted by each electrode, and it is also easy to cause the conductive particles of adjacent electrodes to contact and short circuit; too small conductive particles are easy to form. The problem of particle aggregation results in uneven particle distribution density. In terms of the types of conductive particles, metal powder and polymer plastic balls have been mainly coated with metal. Commonly used metal powders are nickel (Ni), gold (Au), gold-plated nickel, silver and tin alloys.
At present, under the trend of reliability and fine pitch, such as the anisotropic conductive adhesive used in COF and COG construction, the conductive particles of multi-surface nickel-plated and gold-plated polymer plastic powder are characterized by the compressibility of the plastic core. Therefore, the contact area between the electrode and the conductive particles can be increased, and the on-resistance can be reduced. At the same time, the thermal expansion of the plastic core and the resin-based raw materials is relatively close, which can avoid thermal cycling and thermal shock in the high-temperature or low-temperature environment. Due to the difference in thermal expansion between the particles and the resin-based raw material, the contact area between the particles and the electrodes is reduced, leading to an increase in on-resistance and even open circuit failure.
2.5 Lamination process: usually conductive particles are evenly distributed in the adhesive without contacting each other, plus an insulating film, the ACF film is non-conductive. When the ACF film is pressurized and heated (generally pressurized and heated twice) , The first time is temporarily affixed to the product 60 ℃ ～ 100 ℃, (3 ～ 10) × 104 Pa, 2 s ～ 10 s shipped, the second time is about 150 ℃ ～ 200 ℃ when the parts are mounted, (20 ～ 40) × 104 Pa, 10 s ～ 20 s) The conductive particle insulation film is broken and squeezed together with each other in the part where there is a line (because it protrudes from the wireless part) to form conduction, and the volume of the conductive particle after being squeezed 3 to 4 times the original (the volume of the conductive particles does not change, the difference is that the original particles are spherical, after heating, they become like a round cake, so that the upper and lower electrodes have more area to contact the conductive particles) , heating to make the adhesive Cure and keep conducting. Generally, the resistance of the conducting part is below 10 Ω, and the adjacent terminals of the non-conducting part are above 100 MΩ.
ACF brand and differences
3.1 Sony ACF (Single Layer)
Sony developed advanced ACF technology called Microconnector, which is applied to COF and COG joints. This ACF material is a breakthrough development in the production of conductive particles. The conductive particles are generally coated with a metal layer on the surface of the plastic core, and then a 10 nm thick insulating layer is coated on the surface of the metal layer, and the insulating layer is composed of extremely fine resin particles.
The resin adhesive of the development material can be a thermoplastic or thermosetting material, and then conductive particles are added to make a paste or film. When this material is attached to a flexible board substrate for the hot pressing process, the conductive particles and chip bumps and the flexible board substrate electrode will simultaneously break the insulating layer of the contact surface (that is, the Z axis direction), but the XY plane direction that is not contacted The insulating layer will not be crushed and maintain its insulation. Therefore Sony believes that the use of such conductive particles coated with an insulating layer can increase the particle density of anisotropic conductive adhesives, achieve the requirements of fine pitch and low on-resistance, and at the same time, no short circuit will occur.
3.2 Hitachi ACF (Double Layer)
In response to the fine-pitch requirements, Hitachi Chemical has proposed an ACF with a double layer structure. The upper layer of the double layer structure is a resin layer without conductive particles added, while the lower layer is an arrangement containing a single layer of conductive particles. Compared with the traditional single-layer ACF, the double-layer structure can increase the density of particles in the unit contact area of the electrode without increasing the density of conductive particles. The density of particles in the unit contact area is higher, and it is close to the chip bump In the region, the occurrence of short circuits is reduced due to the low local particle density.
In terms of resin adhesives, for reliability considerations, Hitachi Chemicals has chosen to use epoxy systems on its products to improve the material's adhesive strength, glass transition temperature, and moisture resistance.
3.3 3M ACF
3.4 Toshiba ACF
3.5 TeamChem Company ACF16, AC42
Low temperature operation of ACF16: Low temperature storage, 12 months below -15 ° C, 14 days at room temperature, hot pressing temperature of 80 degrees Celsius, can be applied to PET film with low heat resistance, ITO glass substrate.
ACF16 is an anisotropic conductive adhesive film that Haizheng Industry launched in 2010. The biggest difference from the general commercial ACF products is their low temperature operation characteristics. Pre-sticking at room temperature, hot pressing can be completed at 80 ° C. And then the electrical resistance is low, high stability, can withstand high temperature, high humidity and reflow.
During operation, pre-adhere at room temperature, and then heat-press at 80 ° C x 5 seconds-10 seconds.
Please do not use gaskets during pre-adhesion and hot pressing, because gaskets will slow down the heat conduction, resulting in the adhesive film not being able to reach the hot-melt state in a short time, resulting in poor adhesion.
After hot pressing, the resin can be stored slowly at room temperature, so that the resin can slowly and continuously carry out molecular bonding reaction, and its bonding strength can be gradually increased accordingly. If necessary, post-cure reaction can also be used to improve its bonding strength. Post-cure can be used at 90 ° C x 60 minutes. If the product finally needs to be able to pass high temperature re-soldering, it is recommended to use two-stage post-baking: 90 ° C x 30 minutes to 150 ° C x 30 minutes, then the strength can be increased to more than 1.0 kg / cm, which is more durable. Harsh high temperature environment.
This product can be repaired after hot pressing, that is, if the conductivity problem is caused by excessive pulling or poor operation after hot pressing, it can be repaired simply by hot pressing at 80 ° C x 5 seconds. Without the need for heavy industry. If rework is required due to poor alignment, it can be removed simply by wiping with acetone.
After hot pressing, it can be stored at room temperature, so that the resin can slowly and continuously carry out molecular bonding reactions, and its bonding strength can be gradually increased with it. This product is RoHS & Halogen-free compliant and does not contain PFOS & PFOA.
3.6 UPAK ACF
Weifeng is the first mass-produced ACF manufacturer in Greater China. Currently there are two types of products: FOG (FPC on GLASS) and FOB (FPC on PCB). COG (CHIP on GLASS) is already developed but the cost is not too high. Suitable for entering the market.
General hot pressing conditions of ACF need to pay attention to the following:
1. Temperature: refers to the actual material temperature, that is, the actual temperature of the ACF, not the set temperature of the hot press.
2. Seconds: refers to the number of seconds of hot pressing. For example, the conditions of 180 degrees and 15 seconds are required, which means that the actual material temperature of ACF must reach 180 degrees in the 15th second, and the temperature is generally required to rise in the first 2 seconds To reach about 90% of 180 degrees, that is, 172 degrees is considered the standard, and then continue to heat up to reach 180 degrees in the 15th second.
3. Pressure: Generally speaking, there are two calculation methods. The ACF using the non-IC interface is calculated based on the total force that the entire area can bear. The ACF using the IC interface is the total BUMP (electrode) on the IC. The total force of the area is calculated, so people often think that the thermal pressure channel of the IC interface is larger than that of other interfaces. This is why.
ACF reliability requirements
See National Standards GB18910-2008, IEC61747.5
How to save ACF
1. Unopened ACF, storage condition: -10 ~ 5 ℃, its use period is six months after manufacture (the date of manufacture and the validity period of ACF under the storage conditions will be indicated on the trademark).
2. Storage conditions of the unopened product: -10 ~ 5 ℃, its use period is SONY 15 days, HITACH 30 days has been opened and exposed to the air, and the storage time is only 7 days. ﹔ Unopened products if stored in high temperature environment Will shorten its useful life.
3. Accelerate the thermal curing of ACF. If the expired product exceeds the warranty period, the company stipulates that the unopened ACF will continue to be used within one year after it leaves the factory, and will be scrapped after one year. . (Shenzhen Jiecan Technology Co., Ltd.)
3 active carbon fiber
Activated carbon fiber (ACF), also known as fibrous activated carbon, is a highly effective activated adsorption material and environmentally friendly engineering material with better performance than activated carbon. More than 50% of its carbon atoms are located on the inside and outside surfaces, forming a unique adsorption structure, known as surface solids. It is a fibrous precursor, activated by carbonization in a certain procedure. The more developed specific surface area and narrower pore size distribution make it have faster adsorption and desorption speed and larger adsorption capacity, and because it can be easily processed into different shapes such as felt, cloth, paper, etc., and has acid resistance Alkali corrosion resistance makes it widely concerned and in-depth research. Has been widely used in environmental protection, catalysis, medicine, military industry and other fields.
Since the 1962 US patent first involved the subsequent use of activated carbon fiber to filter radioactive iodine radiation in the United States, the research and application of different precursor organic fibers and their activated carbon fibers have developed rapidly. The United States, the United Kingdom, the former Soviet Union, and especially Japan are large countries that research and use ACF, with annual output of nearly 1,000 tons. The domestic ACF research started in the late 1980s, and industrialized devices appeared one after another in the late 1990s. Most are in the laboratory research phase.
Manufacturing method: Different precursor materials, the production process of ACF and the structure of the product are also significantly different. The production of ACF generally involves stabilizing the organic precursor fibers at a low temperature of 200 ° C to 400 ° C, followed by (carbonization) activation. The commonly used activation methods are: physical activation method using CO2 or water vapor, and chemical activation method using ZnCI2, H3PO, H2PO4, KOH. The processing temperature is between 700 ℃ ~ 1 000 ℃, different processing processes (time, temperature, Activating dose, etc.) The corresponding products have different pore structures and properties. The organic fibers used as ACF precursors are mainly cellulose-based, PAN-based, phenol-based, pitch-based, polyvinyl alcohol-based, styrene / olefin copolymers, and lignin fibers. The main commercialization is the first four.
Structural characteristics: Activated carbon fiber is a typical microporous carbon (MPAC), which is considered to be "a combination of ultrafine particles, an irregular structure on the surface, and an extremely narrow space", with a diameter of 10 μm to 30 μm. The pores open directly on the fiber surface, and the ultrafine particles are combined in various ways to form a rich nano-space. The size of these spaces is on the same order of magnitude as the ultrafine particles, thereby creating a large specific surface area. It contains many irregular structures-heterocyclic structures or microstructures with surface functional groups. It has great surface energy, and also creates a powerful molecular field where the micropores interact with the pore wall molecules to provide an adsorbed molecular physics. And chemical changes in high-pressure systems. The diffusion path of the adsorbent to the adsorption site is shorter than that of activated carbon, the driving force is large, and the pore size distribution is concentrated. This is the main reason for the large specific surface area of ACF, the fast adsorption and desorption rate, and the high adsorption efficiency.
Functionalization method: Functionalization mainly meets the efficient adsorption and conversion of specific substances through the control of pore structure and surface chemical modification.
ACF is generally suitable for the adsorption of low molecular weight molecules (MW = 300 or less) in the gas and liquid phases. When the pore size of the adsorbent is about twice the critical size of the adsorbate molecule, the adsorbate is easier to adsorb. The purpose of the pore size adjustment is to make the pores of the ACF equal to the size of the adsorbent molecule. The following methods are usually used: 1) the change of the activation process or the degree of activation (to the nanometer level); Activated, or reactivated by adding metal compounds with ACF (mainly mesopores), the raw fiber has a pore size close to the macropores (macropores) in advance; 3) hydrocarbon pyrolysis is deposited on the pore wall, high temperature post-treatment (make Aperture becomes smaller).
Surface chemical modification mainly changes the surface acidity and basicity of ACF, and introduces or removes certain surface functional groups. Oxygen groups on the surface can be removed (reduced) by high temperature or hydrogenation treatment; acidic surfaces can be obtained by gas phase oxidation and liquid phase oxidation. The modification requires comprehensive consideration of the effects of physical structure and chemical structure.
Article Keywords: Characteristics and application of ACF anisotropic conductive adhesive film