Integrating thinned bare dies with inkjet printing interconnect

Integrating thinned bare dies with inkjet printing interconnect
Technology News |
DoMicro in Belgium has developed a wireless IoT demonstrator with a total height of 0.7mm by using inkjet printing technology.  The technology for integrating dies is one of the key enablers for the realization of new applications in flexible hybrid electronics (FHE) such as in-mold electronics or smart glass. This…
By Nick Flaherty

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DoMicro in Belgium has developed a wireless IoT demonstrator with a total height of 0.7mm by using inkjet printing technology. 

The technology for integrating dies is one of the key enablers for the realization of new applications in flexible hybrid electronics (FHE) such as in-mold electronics or smart glass. This thin form-factor enables smooth integration of functionality in various surfaces, labels and fabrics.  

The inkjet printing technology brings several important capabilities, such as seamless and invisible integration, integration of thinned bare dies on flexible substrates and a reduced number of process steps, says Aart-Jan Hoeven at DoMicro.

The company developed a Bluetooth wireless IoT demonstrator to investige the optimal configuration for die contacting and bonding. 

Several configurations were studied, including a Fan In Ball Grid Array (BGA) configuration by inkjet printing on bare die. An inkjet-printed dielectric is covering the die while keeping the areas at the contact pads open. Next on top silver ink is connecting the bond pads to a BGA pattern on top of the dielectric coating. Alignment and registration of structures are performed through the automatic vision system of the used PixDRO LP50 laboratory printer equipment.

This enabled a face up thinned bare die of a microprocessor to be interconnected on the bond pads. As it is impossible to inkjet print conductive tracks via a steep vertical surface, a dedicated ramp structure is provided to guide and support the inkjet-printed silver conductors. This approach avoids height consuming wire bond loops with glob top or as applied in advanced packaging, a redefinition layer or substrate (RDL) interface.

This ‘die first’ approach results in minimal height for assembling and mounting dies in systems. It enables a good optical alignment of the die before integration and offers a compatibility of material surface interaction. 

IoT devices require the integration of a sensing function, computing processing and radio functionality for operating and communicating remotely from nodes to the network. In line with this, the final step for the realization of the wireless IoT demonstrator was the integration of a microcontroller, a Bluetooth radio Integrated Circuit (IC) and a printed touch sensor on a polyester foil.

The thinned Cypress CY8C20 touch controller has been integrated in the same way as the BLE chip. For sake of the demonstration, the demonstrator is powered by a regular cell battery, but a flat flexible battery could be used for a wearable flat flexible device.

The advantage over standard wire bond interconnection is the ability to print functional circuitry on all kinds of thin and bendable substrates. This form-factor enables smooth integration of functionality in various surfaces and the ability to integrate a bare die chip face up instead of flip chip can expose the sensor side of the chip to the outside in an extremely low height package solution.

On the polymer foil, the thinned BLE IC and the thinned touch controller IC are bonded and contacted in a functional circuit and antenna by inkjet printing technology. Additionally, some SMD passive components were added as well. Powered with the external cell battery this demonstrator is able to show two-way Bluetooth communication with a mobile phone app.

The high accurate inkjet-printed traces are aligned and connected to the fine pitch (60 micron track/gap) bond pad of the IC’s. Passives used are approximately 0,5mm thick (height) as this is commonly available in SMD components. Figure 5 is showing the layout of touch area and electronic circuitry for both MC and BLE including the antenna structure.

The next step was to create the Bluetooth functionality. This was done with a Nordic 51822 Bluetooth low energy (BLE) chip, which was available in thinned bare die version. The integration of this chip with printing has been demonstrated in an existing beacon design.

After powering and testing with the Nordic Blinky app, the functionality is shown while interaction is initiated from the demonstrator device back and forth. The touch area is changing the status message in the app. Touch function is activated by a manual touch area on the sample, the state of the button is shown on the wireless interface. The LED can be switched on/off remotely and activated by a switch on the app.

The demonstrator shows bare dies can be integrated in flexible substrates using inkjet printing for the contacting. This is achieved with a dedicated ramp structure for guiding and supporting the printed silver conductors. This approach eliminates the need for height consuming wire bond loops and enables a Flexible Hybrid Electronics application with thin bendable Bluetooth electronics that can be laminated in a thin flexible and/or wearable product or application. 

DoMicro BV is a technology company providing innovative manufacturing technology, application solutions and micro assembly technology for flexible hybrid electronics (FHE) and micro devices. 

www.domicro.nl 

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