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High performance printing processes for Chip stack assembly

High performance printing processes for Chip stack assembly

High performance printing processes for Chip stack assembly
Scematic of a MOSFED (source TI)

To be able to migrate from precision placement of SMD to Semiconductor packaging a knowledge transfer in several areas of the supply chain is going to take place. We believe that soon many SMD manufacturer will also produce components and supposed to be able to manufacture mid-size or even high quantity batches.

With this newsletter we like to support SMD and Semiconductor manufacturing with information about very efficient, high performance print processes for Semiconductor Packaging. In the coming months we will share experience specifically about the following topics:

Semiconductor Backend Processes

1. Bumping
2. Balling
3. Flux printing
4. Chip assembly
5. Chip stack assembly
6. Pre-bowed Chip assembly
7. Copper Pillar chip assembly
8. Chip moulding and filling
9. Conventional LED assembly
10. Min-LED assembly

Chip stack assembly Process

The difference between wafers and chips lies in the relationship between both components. While the wafer serves as a base for the chip, the chip is implanted in the wafer. Together, they make up the integral part of Semiconductor components that’s commonly used in the field of electronics.
Microchips are made by building up layers of interconnected patterns on a silicon wafer. The microchip manufacturing process involves hundreds of steps and can take up to four months from design to mass production. The process of putting a semiconductor device or integrated circuit in a package of one form or another usually consists of a series of packaging steps that include: die preparation, die attach, wirebonding, encapsulation or sealing, deflash, lead trimming/forming, and lead finish.

Microchips are often flat bonded onto a Leadframe or substrate and then another Chip needs to get mounted on top of this Chip. The flat bonding process is done by adhesive, solder paste or sinter materials. Often the Materials need a curing/reflow/sinter process. The first interconnection between the first chip and the Leadframe/substrate will be heated up more times.
This is not helpful for the connection, because of cracking, intermetallic phases and so on.

By using a High precision printing process you can print directly on the placed microchip. The material deposition for the next layer can be structured and done without any heating process in between.
Structuring of the stencils and print process can even perfom for several layers of Microchips.

For an MOSFED , as an example, can this reduce the number of processes and even gives the capability to manufacture the complete Leadframe-die stack in a production line.

Process steps:

1. Print under first Chip (even possible in a stepped down leadframe)
2. Place first chips layer (high side, low side and controller)
3. Print on top of bottom chips
4. Place the copper clip on top
5. One single reflow process at the end

In attached pictures you can see a schematic and the print on top of the first chip layer before placing the copper clip.

Beside the possibility to print wet on wet paste, customers also get the opportunity to streamline and improve the process flow to more economic manufacturing costs by improved quality yields.

Our Semicon teams at Christian Koenen GmbH have extensive process knowledge to design and manufacture customized Semicon stencils. We are offering service support to perform and test printing processes in our Application Lab. Together with our customers we often perform extensive analysis and checks to prove and prepare printing processes for mass production.

State of the art process equipment and measurement methodology is available to establish and optimize all kind of Wafer printing processes. Please contact our team as soon as you like to learn more about stencil printing for Semicon manufacturing processes.

Scematic of a MOSFED (source TI)
Scematic of a MOSFED (source TI)
Print on chips and leadframe ( wet first print underneath dhe dice)
Print on chips and leadframe (wet first print underneath dhe dice)
Print on chip with already 2 dice and 1 clip placed. All wet paste. Before last clip get´s placed.
Print on chip with already 2 dice and 1 clip placed. All wet paste. Before last clip get´s placed.

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