Technology – three-dimensional integration of semiconductor devices
Aerosol Jet Printing for heterogeneous 3D integration in semiconductor modules
Miniaturisation in the 3rd dimension
Printed 3D interposers completely dispense with lithographic processes. They are based on 3D printing. It is an additive process in which - contrary to usual printing processes - it is not only about ink coverage, but in which a volume is printed on. The aim is to create a three-dimensional solid.
First, an insulating layer is printed, which is not applied to the surfaces to be contacted. Here, the printing medium is cured immediately after printing by means of suitable radiation (UV light). This first layer also ensures homogenised surface properties on the wafer surface, which can be better controlled, for example, with regard to their adhesion properties. In addition, this first layer is also intended to compensate for the zone of influence of a laser.
After printing this first insulating layer, these contact surfaces are contacted by means of the metallic ink and a first layer of conductive tracks is printed. A jet printing process is used and the printing medium is cured or sintered by means of a directly tracked laser.
Subsequently, another insulating layer is printed, this time leaving the contact areas open at other predetermined points.
Thanks to the layers lying on top of each other and insulated from each other except for the contact surfaces, it is possible for conductive paths to intersect. Once all layers have been printed, the last layer in turn has contact surfaces that are to be used for contacting a component lying on top.
To facilitate contacting, a vertical elevation of the contacts can be printed analogous to the usual bumps by printing metallic ink several times and sintering each time.
Printing process for the production of 3D interposers
- The printing process for both the conductive and the insulating material can be based on the ink jet principle, which is already widely used and is also applied in 3D printing..
- In addition, there are a number of other printing processes and nozzles that appear suitable.
- A conflict of objectives arises due to the fact that, for economic reasons, a surface or a distance has to be printed in the shortest possible time and due to the fact that the demand for geometric accuracy can only be achieved by very measured application.
- It can therefore make sense to work with several print nozzles that are optimised differently or can be controlled flexibly and change their print parameters in the process.
- The combination of several printing processes, such as screen printing and aerosol jet printing, also appears promising.
Screen printing
Large areas that are to be provided with an electrical layer can be printed using the screen-printing process. The combination with aerosol printing is interesting - this would enable a quick and economical change of print jobs with high flexibility.
Inkjet printing
The advantage of inkjet printing is the high accuracy combined with the possibility to print specific areas thicker. However, there is a risk that isolated drops may not be printed - conductive structures in a printed interposer would be interrupted and the contacting would be faulty.
Aerosol printing
Another nozzle printing process is aerosol printing. This new technology is becoming increasingly important.
As a continuous jet printing process, the risk of discontinuity of material application is greatly reduced. At the same time, the reliability and quality of the conductive structures is substantially increased.
Technical comparison of printed interposers versus SI interposers
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Time-to-market |
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Flexibility |
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3D interposer - process implementation
& optimal integration into the process chain
The printing of 3D interposers can easily be integrated into the existing processes at semiconductor manufacturers:
- On the one hand, it is basically possible to print the interposer on already singular components. This is a very practical approach for smaller quantities. This method would be less ideal for large quantities, as the handling and alignment of the individual components would take a considerable amount of time.
- A more practical approach would be to print the interposer on the homogeneous wafer or on the already separated - i.e. sawn - wafer, as long as the components are still present in the wafer compound. In this case, the advantage would be that the wafer would only have to be handled and aligned once.
- For optimal accuracy, it would be advantageous if the wafer was not yet sawn, but already laminated on the sawing foil.
The printing of an interposer can take place within a technical system in which all the necessary steps take place without the wafer or the component having to be removed again until the interposer is finished.
