Advancing Semiconductor Packaging: The Role And Anatomy Of Interposers In Modern Technology

By Author: Ryan
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Package advancement is the reason modern semiconductors exist as today’s semiconductor products are only made possible by new packages. The concept of heterogeneously integrated components involves the use of a structure called an interposer that holds electrical connections between dies or elements within the package. These structures are similar to PCBs due to the fact they act as a base of the system on which several components can be incorporated into one package. In terms of design, much more flexibility can be achieved on an interposer board.


While interposers give the packaging designers some freedom as to how they stack and integrate 2.5D and 3D components, there are complications when it comes to an interposer. EDA tools for IC and PCB design can still not automate these important tasks for interposer design fully, partly because there is still new development in the field and interposer structures are not completely standardized yet.


Anatomy of an Interposer


Interposers for advanced packages require precise design and the shape is made according to a chip package ...
... and a package substrate. Therefore, it can be like comparing an interposer to an electronics bare printed circuit board (), a structure where a complete package shall be developed.


Due to the need to provide semiconductor dies in heterogeneously integrated components


To allow interconnection between semiconductor dies to occur


For rejoining the whole stack to a packaging substrate


It has an array of SHH (small horizontal holes known as through-silicon via or TSV) and small pads for volts connections to the semiconductor die in the package. The interposer also extends to the package substrate, which can provide more signal paths both between parts and out of the package. One side of the substrate has several solder balls (BGA format) which can be mounted on the land pattern on the PCB.


Between the TSV region and the micro bumps on the top layer of the interposer is the redistribution layer or RDL. The interconnection structure of an RDL is similar to the blind/buried microvias in an HDI PCB arrangement.


Interposers are generally made from three possible materials: substrate material of silicon, glass, or any organic material. Interposer or Pre-IFS is a fully fabricated component in foundries such as TSMC, and it consists of TSV and horizontal interconnection, which will connect to the package substrate as well as to the semiconductor die. The interposer can be designed to function in two ways: as an active or passive component.


Interposers can be prepared from materials and in different ways, although they have some shared properties. Interposers are fabricated from copper-clad laminate (CCL), epoxy prepregs, glass fiber polyester reinforced (GFPRP), or other suitable materials. The CCL material is most often situated on the outer layers of the PCB, and holes are made using a laser through the material with subsequent plating. After the formation of an interposer, it is then placed on the bottom side of the PCB.


In addition, the interposer can be fabricated either manually or through the use of various fabrication technologies. The issue with making PCBs is that it still largely relies mostly on manual procedures such as PCB drilling, plating, lamination, and etching. Others are the drilling, platinizing, laminating, etching, and pick and place processes.


The first two types are known as active interposer board and passive interposers depending on how they function.


Passive interposers have a simple function: to offer electrical connections between dies on the top side of the interposer. The only difference with these components is that they do have conductive tracks but no electronic circuit. It is just a mechanical frame that has conductive pathways for the signal to pass through.


These are insulating substrate materials and thus can only act as conductive interconnect carriers throughout the package for other components like organic material and glass. This is so because silicon serves as a semiconductor and through the use of active interposers, devices will always be inserted in the silicon formation. These interposers must have a lesser number of TSVs because of keep-out placement in the structure. Some of the regular devices that may make up the active interposers could be the DC-DC converters together with the I/O interface controllers.


Packaging Substrate


The other component that is included in this package is the package substrate. If you examine the image above and pay attention to the cross-section of the lower substrate, you will realize that it appears to resemble the inside of a PCB. The interposer includes minute ball contacts, and the substrate transmits these contacts between the dies placed on the interposer. These two connections extend down to a bottom surface where several balls in the Ball Grid Array or BGA are soldered accordingly.


Interposer-based components in an electronics assembly


Interposers are basic structures that have contributed to pushing up innovation in complex packaging and the continued integration of elements in restricted volumes. However, all chip packages cannot make sense if they are not incorporated into a PCB assembly with other parts. For higher-density interposer-based components, it will be important for PCB designers to determine the location of a BGA along with coming fan out and escape routing standards.


A few points should be remembered:


• Stackup design will many a time create specific routing requirements, such as trace width for impedance-controlled signals


• Via pitch can limit the available space for escape routing, sometimes, via-in-pad may be necessary


• Review your fabrication house specifications to make sure your stack up and via design are doable at their shop


Interposers or interposer connectors are a class of compression-mounted interconnect devices located between the boards or sockets through which an electrical signal can pass in a very short time. They are nominally larger than a standard connector, which makes the rerouting of connections simple, and gives the designer a versatile, easily replaceable faceplate. The wide pitch accommodates a much larger channel for the passing of electrical signals thereby utilizing less energy in the passage of signals and enhancing the minimization of RC delay also units in a system are well separated. Some can be very thin which makes them fit in small packages and hence serve. Some interposers have spring pin technology. Interposers are typically used in the spaces of the BGAs or multichip modules. There are also optical interposers available in the market for implementing interposer operation. They are used in fabrication because they permit the structure of intricate circuits to be established in a short time, without having to originate each constituent individually.


Three materials are used for interposers: Si, oxide, and organic substances. Therefore, silicon is a known material and widely used, but it is thermally and cost-effective. Glass has lower cost by maintaining high density and it has even less thermal conductivity and there is a high risk of cracking during manufacturing. Organic materials due to their lower pitch and lack of mechanical rigidity offer less resistance. Glass and organic interposer boards are still young technologies, and much remains to be done in their development.

High Quality PCB Co., Limited is a leading PCB(Printed Circuit Board) Manufacturer in China since 1995. Dedicated to the technologies innovation, being engaged in IC Substrates, High-Density Interconnect PCB, Multi-layer PCB, Rigid Flexible PCB, Flexible, Radiofrequency PCB.