In 2006 RFID – the keyword and hope of many users, particularly in supply chain management and logistics processes, took a short break in development for technological and also systematic reasons.Basically, technological challenges (e. g. in the field of UHF) were clarified in 2006. And due to ageneral and worldwide broadening of RFID applications, the value proposition RFID means forproduction, logistics and anti-counterfeiting could be made clear to a wide spectrum of users. The horizontal expansion to a wide range of users and the knowledge gained on the realization of RFID technology are the signs for a sustainable enhancement in 2007.

In the value chain, DELO Industrial Adhesives considerably contributes to meeting the requirements regarding productivity in the RFID inlay production as well as product quality of the inlays in the application. The adhesives DELO has researched and developed for contacting the chip to the antenna substrate play a major role for the efficiency of HF and UHF inlays.

In order to explain the adhesive’s tasks more clearly, a reel-to-reel production process of RFID inlaysis exemplarily illustrated below.

Illustration 1

Exemplary illustration of a typical production process for RFID inlays: In the first step, the adhesive is applied. Then, the chip is placed. Afterwards, contacting is ensured in the subsequent thermodestation.

The antenna produced in a preprocess is fed to the production machine from a roll. The antennas are mostly made of PET basic laminates, either with copper or aluminium metallization. Moreover,antennas printed with silver inks are available. Paper- or polyimide-based antennas are commonsubstrate variants.

Production in cycles tuned to seconds

The first step of the inlay production is the adhesive application to the contact surface of the antenna,to which the chip is to be attached later. The adhesive is either applied through needle dispensing, or by means of screen printing, as shown in illustration 1, in the case of parallel antennas on the substrate, that is to say larger web widths. Afterwards, the chip is placed from the wafer to the antenna into the adhesive with the flip-chip method. This procedure is applied as the active side of the chip with the bumps (contacting areas) is open and directs upwards after chip production, and
functionality is only achieved if this side faces the antenna so that the chip must be “flipped”.

The placement of the chip is followed by a buffer station in order to subsequently cure the adhesive in a thermode station (see illustration 2). In doing so, the temperature is added to the system with an upper and a lower heated plunger (thermode). Besides heat addition, the thermodes fulfill the function of pressing the chip to the antenna under defined force, ensuring electrical contacting. Afterwards, one inspection step (functionality test) is interposed in order to detect possibly missing components and make them recognizable for the following processes (e. g. conversion to a label).

Illustration 2

In the thermode station, the chip is pressed onto the antenna in order to achieve contacting and cure the adhesive in position through heat addition.

In principle, the adhesive – either a non-conductive die attach adhesive or an anisotropic conductive (in one spatial direction) product – undertakes the task of reliably fixing the microchip to the antenna at a defined position. Besides purely mechanical tasks, the adhesive ensures electrical contacting, additionally.

In case of chips with stud or Pd bumps (illustration 3), electrical contacting is only indirectly reachedby the adhesive. These bump variants are distinguished by a very sharp-edged geometry and inhomogeneous surfaces so that the bumps directly penetrate the metallization layer when placing the chip onto the antenna substrate, closing the electrical contact. The adhesive in the form of a nonconductive product (NCP = Non Conductive Paste) only ensures the chip’s position accuracy in all three spatial directions in this case. Even minimal lifting of the chip from the substrate opens the contact and would lead to a functional deficiency of the inlay.

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