No matter if cash registers in supermarkets, luggage labels at airports or labels of parcels or letters are concerned – up to now the barcode has been the most common and fastest method to read encrypted information such as prices or addresses. The rapid progress in the field of microchips and the development of a completely new technology, the Radio Frequency Identification (RFID), associated with it offer previously unimaginable opportunities in the field of data storage and protection. Due to RFID, mainly logistics companies benefit from a decisive acceleration and facilitation of storage management. Moreover, the information saved on the chip can not only be read without contact by means of radio waves, but also extended by further contents. This new technology allows companies to gain a detailed overview of their current stock as automatic booking of the goods in stock is provided.

This is enabled by the use of a so-called smart label, a label with semi-conductor chip and antenna, to which data in the HF (high frequency; 13.56 MHz) or UHF (ultra high frequency; 860-930 MHz) range is transferred.

In the near future the demand for smart labels will increase significantly. Thus, the demand for economical and efficient production methods is becoming more and more important for semiconductor manufacturer as well as label and logistics suppliers. Bonding of the semi-conductor chip to the label is a crucial production step. In this field, the so-called NCA (non-conductive adhesives) and ACA (anisotropic conductive adhesives) adhesives provided by DELO Industrial adhesives offer an effective solution already successfully realized millionfold in practice due to their reliable connection of semi-conductor chip and antenna in seconds.

From COB process to flip-chip technology

For numerous applications in the smart card sector as well as for smart labels initially, the so-called COB (chip on board) or COF (chip on flex) technologies represented the preferred process for the mechanical and electrical connection of semi-conductor and substrate.

With this technique, the chip is mechanically fixed to a substrate and electrically contacted in a socalled wire bond process with gold wires. Then, the contacts are protected against environmental influenced by encapsulating the chip and the wire bonds. Standard encapsulation compounds are cured by light or heat. The curing times range from 30 seconds to 2 hours at temperatures from room temperature up to 200 °C.

For contacting bare semi-conductor chips in smart label applications, however, this complex and relatively slow process is not an adequate solution. Considering the long curing times, the production of several billions of RFID labels per year would be unthinkable.

Here, the advantages of the so-called flip-chip technology come into play enabling easy, economical and fast contacting of chips on miscellaneous substrates. In the flip-chip technology, a semiconductor chip is already equipped with so-called bumps on its structured, active side by the manufacturer. Then, the chip refined with bumps is pressed into the substrate metallization with its active side facing the substrate.