1. Introduction ESD has a very large impact on the entire semiconductor industry. The annual economic loss of the semiconductor industry due to ESD is in the billions of dollars. With the gradual and in-depth promotion of gold card engineering and IC card localization in China, the influence of ESD on IC card module packaging such integrated circuit package form has become a research topic.
What is the mechanism of ESD production? What is the impact of its impact on the IC card module package? What measures should be taken to improve or eliminate these effects? This paper makes a preliminary discussion on the above issues, and combines the practical examples of Shanghai Schlumberger Smart Card Technology Co., Ltd. to propose several simple measures to control the impact of ESD.
2. ESD and the cause of the constituent atoms of the substance contain electrons and protons. When a substance acquires or loses electrons, the substance appears to be positively or negatively charged. Static electricity is the result of the accumulation of positive or negative charges on the surface of a substance. Charge accumulation is usually caused by contact, separation or friction of matter, commonly referred to as triboelectric generation. There are many factors that affect charge accumulation, including the degree of contact of the object, the coefficient of friction, and the rate of separation. Before the influencing factors are eliminated, the charge will continue to accumulate, then be released, or accumulate until the insulation properties of the surrounding material or the insulation protection fails. Once the insulation properties are changed, the electrostatic balance is quickly achieved.
ESD (Electrostatic Storage Deflection) is a rapid balance of charge, and the rapid balance of charge is called electrostatic discharge. Studies have shown that people walking on carpets can generate static voltages of up to 20KV due to the charge generated by friction. Since the charge is released quickly with little resistance, the equivalent current when released can exceed 20 amps. If it is discharged through an integrated circuit or other ESD-sensitive components, then a large current is likely to severely damage a line that would otherwise conduct a microamp or milliampere current.
3. The impact of ESD on IC card module packaging The impact of ESD lies in the entire life cycle of integrated circuits for wafer fabrication, integrated circuit packaging, device testing, assembly and use. For whatever reason, ESD is generated as long as the charge builds up on or around the device. The economic losses of the semiconductor industry caused by ESD each year are as high as several billion dollars.
Integrated circuit devices are very sensitive to ESD. Integrated circuit devices should operate within certain voltage, current, and power dissipation limits. A large amount of static charge will generate high-voltage discharge when conditions are suitable (such as air humidity above 65%, or operator contact, etc.), and electrostatic discharge will be transmitted through the high-voltage transient of the device leads, which may cause the oxide layer (ie, insulator). Disconnected, causing the device to malfunction. When a large electrostatic current flows through the PN junction, the PN junction temperature rises sharply due to heat dissipation. The thermal time constant of a semiconductor is generally longer than the transient time of an ESD pulse. It is difficult for heat to diffuse rapidly. If a large current is generated by ESD, the metal interconnection will melt and damage the PN junction of the device, causing the device to overheat and fail. ESD can also trigger silicon controlled rectifiers to create latchups in CMOS devices. Under normal conditions, ESD does not cause immediate failure of the device. It is often lurking in integrated circuit devices. This potentially defective device is very susceptible to failure when used.
IC card (Integrated Circuit Card), also known as smart card, integrates integrated circuit chips with storage, encryption and data processing capabilities into plastic substrates, involving microelectronics, computer technology and information security technologies. As a mature high-tech product, IC card has improved the modernization of people's life and work, and has become one of the symbols of a country's scientific and technological development level. IC cards have been widely used in telecommunications, finance, transportation, medical and government utilities in foreign countries. Thanks to the strong promotion of the Ministry of Information Industry and China Telecom Group, the application of IC cards in China, especially in the field of telecommunications, has made rapid progress.
The IC card module is the core of the IC card and is a form of integrated circuit package. The basic manufacturing process of the IC card module is very similar to that of a conventional integrated circuit package, and consists of DieBonding, WireBonding, Encapsulation, and Testing. The difference is that the used carrier tape (LeadFrame) is a soft base strip with copper substrate and nickel and gold plated on the epoxy substrate. It is similar to the flexible package (Flexible Substrate) used in advanced packaging such as TBGA and CSP. The input and output of each process of the card module package are wound on a specific reel.
The integrated circuit chip packaged by the IC card module is a crystallization of the development of integrated circuit technology with fine refinement and high integration. Because the distance between devices is as small as micron, the effect of ESD is particularly prominent. Once the electrostatic discharge breaks down, the consequences are very serious. Although circuit designers can use the necessary protective devices, such as Zener diodes, filters, etc. to minimize the effects of ESD, the static build-up on production equipment, in the production environment, and on the operator remains on the silicon. There is still the possibility of short-circuit breakdown during packaging, which may damage the performance of the device and result in a decrease in yield.
4, countermeasures and examples In addition to the protection measures in the design of integrated circuits, the measures to eliminate the impact of ESD are concentrated in the production equipment and production environment.
4.1 The advancement of automatic packaging equipment for production equipment has made electrostatic problems more and more prominent. Many packaging equipment can reach a production rate of 20,000 per hour. If the design is unreasonable, a large amount of static electricity generated in a short period of time will damage a large number of devices. The IC card module packaging device uses a large number of stepping systems such as rails and slides, and uses a robot arm or other clamping device to form a picking system. If the device is not designed properly, the stepper system and the pick-up system will accumulate a large amount of charge and discharge during the transfer. To prevent ESD from occurring, the equipment needs to select the appropriate materials, clamping devices, proper process and grounding.
In IC card module packaging equipment, some components are made of plastic or plastic composites. The manufacturing process must incorporate additives and adjust the proportion of additives so that the plastic or plastic composites obtain a certain degree of conductivity and dissipation (conductive materials). Refers to materials with a surface resistivity of less than 106 Ω/m2, and dissipative materials refer to materials with a surface resistivity of less than 1012 Ω/m2. In addition to this, the additive can also increase the hardness of the material. In addition, the plastic cover used on the equipment should be made of dissipative materials or use conductive or dissipative paint to prevent triboelectric generation.
In the production of IC card modules, various protective tapes must be used to protect semi-finished and finished products. The patch, wire bonding and packaging processes use a toothed protective tape, which is then used to protect the finished product. The protective tape should be made of a dissipative material. Since the IC card module uses a soft base strip as the carrier tape, the production organization is generally carried out by roll-to-roll, and the disk for winding should also be made of a conductive material or a dissipative material. And the disc to be wound, the load-bearing bracket and the equipment rack must be connected to the ground, otherwise ESD will be caused by the potential difference.
The positioning device, the track and the sliding device constitute a stepping system for the IC card module package. Under the premise that these devices or components are interconnected and grounded to the equipment rack, the strips should remain interconnected with the stepper system in stepping. The IC card chip is very sensitive to ESD, and the positioning device, the guide rail and the sliding device cannot be directly fabricated using materials such as nylon.
The nozzle of the pick-up chip used for the patch should be made of a dissipative material and should be well grounded, otherwise there is a possibility that static charge buildup will damage the chip.
The device must have a good grounding device to dissipate the accumulated charge. If there is no ground, the conductive parts will accumulate charge. If the hinge is poorly grounded, the dissipative plastic cover will also accumulate charge. The hinge may be corroded and become an insulator or generate a large electrical resistance. Therefore, a braided ground strap is required to ground the hinge of the rack and the dissipative housing. The surface of the device should be electrically conductive or plated. If conductive coatings cannot be used for design reasons, a braided ground strap should be installed between the two surfaces. If the optional components of the device are connected to the main body of the device, a grounding device must be used to maintain the potential balance of the entire machine. The grounding wire is not a substitute for the braided grounding strap because the grounding strap has a large surface area that can release more charge and the electric field generated by the braided ground strap is minimized.
4.2 Production environment The IC card module package purification workshop shall carry out all-dimensional anti-static treatment of the three-dimensional space, and control the materials, temperature and humidity of the four walls, ceiling and floor.
In the current purification plant, dust generated by fear of friction often uses some hard wear-resistant materials for construction and decoration materials, and these materials are often very easy to generate static electricity, which is contradictory. One solution is that the walls and ceilings of the entire purification plant dissipate the accumulated static charge through an anti-static floor made of dissipative material.
High or low relative humidity can exacerbate the effects of ESD. Experiments show that when the relative humidity is lower than 45%, the static charge generated by friction is several times higher than the static charge in the environment of 55% relative humidity. When the relative humidity is higher than 65%, the probability of electrostatic discharge is significantly increased. Therefore, while the IC card module packaging plant controls the 10,000-level purification level, it also needs to select a good constant temperature and humidity control system to strictly control the temperature and humidity of the workshop.
The fiber dust in the IC production workshop due to the friction of the airflow and the clean clothes of the workers is still electrostatically charged. These fiber dusts accumulate on the operator, and the ESD influence is generated by the contact of the operator with the IC card module device.
Therefore, the operator's clean clothes should be dissipative, and use the wrist strap to connect the body to the device during operation.
4.3 Example Shanghai Schlumberger Smart Card Technology Co., Ltd. (formerly Shanghai Jinchangcheng Smart Card Co., Ltd.) is an enterprise designated by the Ministry of Information Industry to produce prepaid calling card modules and mobile communication GSM SIM cards. The company's business scope includes designing and producing smart cards such as telephone card modules and SIM cards, selling self-produced products, providing maintenance, installation and consulting services. At the beginning of its establishment, the company attached great importance to product quality control, established a strict and comprehensive quality management system, and successfully passed a series of certifications organized by the Ministry of Information Industry. In the past two years of production practice, the company's products in routine testing and resistance to mechanical damage (slice shear force, gold wire pull and ball shear force) inspection, high temperature storage test, high and low temperature impact test and high temperature and high pressure steam Under the control of a series of quality testing methods that are ahead of the industry peers, tests by internationally renowned companies such as STMicroelectronics and Yiheng have reached a high level and have gained the trust of users.
How to minimize the impact of ESD in the production process is also an important research topic of quality control. In combination with the above countermeasures to eliminate the influence of ESD, Shanghai Schlumberger Smart Card Technology Co., Ltd. has explored both production equipment transformation and production environment control, and better controlled the impact of ESD. Shanghai Schlumberger Smart Card Technology Co., Ltd. IC card module production equipment imported from France and Switzerland, respectively, has achieved a high level of stability and accuracy. After a period of production observation, some plastic parts on the equipment were modified to further improve the performance of ESD resistance. The key parts, such as the plastic parts of the step guides, are strictly measured, except for the dissipative requirements, and the rest are replaced by metal parts. The connection of the load-bearing brackets of the input and output reels to the equipment has been reinforced. The original imported plastic reel was redesigned into a metal reel, which improved productivity and stability in addition to improved ESD performance. Shanghai Schlumberger Smart Card Technology Co., Ltd. IC card module production workshop constant temperature and humidity, temperature and humidity are controlled within the range of 21 ° C ~ 25 ° C, 45% ~ 65%, such temperature and humidity conditions limit the impact of ESD. Anti-static floors are laid in the workshop and outside corridor areas to dissipate static charges that may accumulate in time. The actual results were measured using special equipment, and the measurement results show that the above measures are feasible.
Of course, the impact of ESD is difficult to completely eliminate. With the further development of production practices, the control accuracy will be further improved, and new phenomena will gradually appear and be improved or solved. As other core technologies are gradually mastered, the booming development of IC card applications will become a new bright spot.
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