Analysis of smart card contactless module packaging technology

1. Introduction to smart card module packaging technology

The smart card is an integrated circuit chip card that conforms to the IS07810 and 7816 specifications. The French Roland Moreno was invented in 1974. Since then, after decades of development, smart cards have entered all areas of our lives.

According to the data transmission method, the smart card can be divided into a contact card, a contactless card and a dual interface smart card (Hybridcard or Combi-card). The most commonly used form of contact smart card is mobile phone SIM card; the most common form of contactless smart card is bus card; dual interface smart card is now just in its infancy, and will be mainly used in financial bank cards in the future.

As a key part of the smart card industry chain, smart card module packaging plays a decisive role in the quality of smart card products. The smart card chip is designed by the chip design company and then sent to the chip manufacturing company. The chip production company first processes it into a wafer, and then cuts it into a number of separate chips, using epoxy glue. The chip and the substrate (1eadframe) are fixed by heating (this process is called Die Attaching).

Then, using a gold wire having a diameter of 1 mi1 (gold content of 99.99%), the pad on the chip is connected to the second pad on the carrier tape (this process is called wire bonding). Then, the epoxy resin molding compound (EMC) or the epoxy resin encapsulant (UV-curing encapsulant) is used to wrap the chip and the gold wire to protect the chip and the gold wire (this process is called The molding process Molding or the dispensing process (Encapsulation), the product at this time is called a smart card module. Finally, the electrical performance of the packaged module is tested, and the problematic module is selected (this process is called electrical performance test procedure, Electrocal Performance Testing).

The smart card package includes the above-described patching process, wire bonding process, molding or dispensing process, and electrical property testing process. Depending on the type of product, contact and non-contact products are different in the way of protecting the chip and gold wire in the molding or dispensing process. The contact product is protected by the use of an epoxy resin filler containing uV (ultraviolet) light on the surface of the chip and the gold wire to be solidified by UV irradiation. The non-contact type is made of a heat sensitive epoxy resin. The material adheres to the surface of the chip and the gold wire and is heated to 175 ° C to cure to a solid.

2. Non-contact module packaging trends and the dilemmas faced

With the development of technology, the application fields of contactless smart cards are becoming more and more wide. The second generation of resident identity and bus card in China are the practical applications of contactless smart cards.

According to the development of Moore's Law, the size of the chip is moving toward two extremes. For function-fixed applications, the chip size is originally smaller (chip slze is already below 0.5mm*0.5mm); for functions becoming more and more complex Application, the chip size is getting larger and larger (chiP Size has exceeded 3.5mm*3.5mm). The standard size of the chip pad on which the chip is placed on the substrate is 3.5 ram * 3.4 mm.

In the face of a small-sized chip, there is a case where the distance between the gold wire from the solder joint on the chip to the second solder joint on the substrate is too long, and the stability of the arc over the long arc height is worse. The fluctuation range of the arc height should be controlled between 90um and 120um, which is a big challenge for the wire bonding process. The choice of the curve and the optimization of the various process parameters must be in place. In the process of connecting the gold wire to the second solder joint, the vertical distance between the gold wire and the chip pad edge is less than 30um, and the heat-sensitive epoxy liquid impacts the gold wire in the subsequent molding process. When the Uchip pad touches, if this happens, the non-contact module will fail and cause unavoidable loss. In the case where the chip size exceeds the chip pad, after the molding is completed, the problem that the edge of the chip is damaged by the touch of the substrate and the non-contact module is ineffective is also caused, which also causes unavoidable loss.

In addition to the above two problems, a common problem with the non-contact module package is that the second solder joint is prone to be separated from the gold wire after the molding and electrical performance test procedures. This situation has a lot to do with the substrate and the nature of the EMC itself. The substrate is stamped from a 60° or 80um thick copper foil and the surface is evenly plated with a very thin layer of silver. Since the silver on the surface of the substrate is very easily oxidized, the gold wire is prone to bond and insufficient during the bonding of the silver on the substrate under the action of heating, impact force and ultrasonic waves, resulting in an occurrence of a virtual break. Further, in the production process of the subsequent process, the failure of the non-contact module is unsatisfactory due to the large difference in the thermal expansion coefficient between the EMC and the substrate and the gold wire, and the mechanical property of the temperature becoming large.

3. Solution to problems faced by non-contact module packaging

For the case where the chip size is too small, the chip can be placed on the side of the chip pad that is biased toward the second solder joint. For the product whose chip size is about 0.5mm*O.5mm, the chip is attached to the chip pad center in the patch process. It is about 0.3-0.4mm on the side of the second solder joint. Shortening the thread of the line arc can largely solve the problem that the arc length is too long and the arc height is unstable, and the gold wire can be improved to some extent. The vertical distance from the edge of the chip pad prevents the module from failing due to the touch of the gold wire and the chippad edge.

There are two solutions for the case where the chip size is too large. One is to design a matching substrate specifically for this chip design, but this solution is expensive and has a long cycle. It is not feasible for conventional small batch applications, and requires glue used in the patch process ( Die, attachadhesive) to make adjustments. The diameter of the spacer particles in the glue directly controls the thickness of the glue layer. Conventional use of spacer particles with a diameter of 10-15 μm, replacing it with spacer particles with a diameter of 25-45 μm, can increase the thickness of the adhesive layer by 10-20 μm, which can largely avoid the chip touching the substrate. The situation occurs, which in turn prevents module failures from occurring.

For the second solder joint, the firmness is unstable, and the virtual break is prone to occur. The gold wire and the substrate used are incapable of being changed, and can only be optimized from the used wire bonding process. In order to avoid the occurrence of similar situations, it is possible to solder on the second solder joint of the substrate and cut it off before connecting the soldering point on the chip with a gold wire, and then start the solder joint on the conventional soldering chip. The second solder joint on the substrate is then soldered. By this method, the contact area between the substrate and the gold ball (Free Air BaH, FAB) can be enlarged, and the bond between the gold wire and the substrate can be more fully realized, and the welding can be performed again. The second solder joint realizes the molecular bond between the gold wire and the gold ball on the substrate, thereby largely avoiding the internal fusion failure, resulting in the occurrence of a virtual break. One advantage that comes with this solution is that the vertical distance between the gold wire and the chiPpad is increased (15-20tua can be increased), which can better avoid the occurrence of gold wire and chip during the processing of the subsequent process. The touch of the pad edge causes the module to fail.

4. Summary

In the future, the packaging form of smart cards will be more diversified. It is believed that more and more new technologies and technologies will emerge in the future, and the functions of smart cards will continue to increase and the cost will gradually decrease.

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