The trend toward miniaturization and functional integration in the electronic industry is unbeaten. 3D-packaging, Package on Package (PoP) or System in Package (SiP) are key technologies to realize high functional integration into the smallest space, but PoP or SiP deal with packaging on chip level only. The chip itself has to be assembled to a substrate and this substrate in his turn has to be connected electrically and also mechanically to his environment. The solution for the 3D assembly and 3D connectivity is offered by the 3D-MID technology (MID = Molded Interconnect Devices).
3D-Packaging and MEMS integration
In this article the 3D-MID technology and its benefits for MEMS packaging will be explained.
The 3D-MID technology, which is already applied in several connectivity solutions, is coming in increasing use for MEMS integration. 3D-MID allows miniaturization by the integration of mechanical and electronic functions in one part and so much more compact construction and much greater function density can be achieved. More and more applications involving electrical and electro-optical circuits are made using 3D-MID technology. Typical targeted applications are: Sensor packaging, LED packaging, security casings, RFIDs and antennas.
There are several possibilities to manufacture 3D-MID products. However, the LDS (Laser Direct Structuring) process is the most widespread 3D-MID process. Hundreds of millions of mobile phone antennas are manufactured by the LDS process year for year. In addition to the manufacturing of antennas, which consist only in 3D substrates (without electronic assembly), the 3D-MID technology, thanks to its capability to integrate mechanical and electrical functions in one module, unfolds its real strengths in applications with electronic assembly like MEMS packaging as well as LEDs.
3D-MID process steps
Plastic parts acting as substrates are manufactured by a single shot injection mold of plastic material doped with a metal-complex. Material choice is done according to application requirements (e.g. Temperature, SMT capability etc.).
After the injection molding the structuring of the layout on the plastic parts takes place by laser. A laser ray activates on the one hand the doped metal complex in the plastic material and on the other hand ensures a keying of the plastic materials on the structured areas. Further treatment of the laser structured area is needed, if bonding or flip-chip on the final surface is required (ultrasonic- or thermo-mechanical stamping or CO2-cleaning). Such a treatment is need for smoothing rough areas/pads intended to be bonded.
Standard layers for chemical plating are Cu/Ni-P/Au. Other layers are also possible. The plating process is the most sensitive process step in the 3D-MID manufacturing chain. More than 80 parameters have to be monitored and controlled, most of them even continuously. Bath parameters have to be adapted according to material type and part geometry.
Electronic assembly on 3D-MID is similar to the PCB electronic assembly. Soldering, conductive adhesive, bonding and flip-chip are possible. A combination of MID on PCB or PCB on MID is also possible. The greatest challenge in comparison with the PCB electronic assembly is the 3D positioning and fixing of the electronic components on the substrate during the assembly process. Sofisticated 3D-MID assembly machines are available on the market and the development in this sector is proceeding apace.
The high temperature during the soldering process is another challenge which has to be taken in consideration because of the different CTE (coefficient of thermal expansion) of the plastic subrtrate and the metall layer. However, this poses no problem provided the individual steps in the process are optimally adjusted with one another from design and molding making through laser structuring and metallization to the final assembled product. 3D-MID products used e.g. in automotive applications fulfill the highest automotive standard regarding reliability, withstanding the toughest environmental tests (> 1000 temperature cycles from -40°c up to 150°C).
Main drivers of the 3D-MID
The main drivers of the 3D-MID Technology are:
• Miniaturization: Opportunity to solve space problems, e.g. in applications for automotive, medical, mobile application like mobile phones
• Rationalization and system simplifi cation: Reduction of process steps, number of parts and mounting time
• Functionality: New additional functions possible due to various functional integration options, design flexibility and precision provided by 3D-MID
Benefits and potential use of 3D-MID
The 3D-MID technology offers a real opportunity for MEMS applications due to its capabilities regarding miniaturization. In particular for packaging, where positioning tolerances and the mechanical and electrical connection to the environment lead to high challenges, the 3D-MID Technology provides the right packaging solution.