Wafer Level Packaging, also known as WLP, is a subcategory of IC packaging technique that is suitable for wafer level. You cannot cut the wafer without packaging. Instead, it is important to first cover the wafers with packaging and then cut them through.
Before cutting the wafer, it is important to add special bumps while assembling the components. WLP is a simple and cost-efficient process. There are different steps in the WLP that need precision.
These are wafer fabrication, wafer testing, and analysis. WLP is also reliable when you need to make sure everything is in place, from procuring the raw materials to shipping the final product to the customers.
The process is also known as Chip scale packaging and can be divided into two further sub-categories called fan-in and fan-out packaging.
In the past times, people used wires to combine the semiconductor chips and their substrate together.
It is important to do this on the periphery of the semiconductor as problems majorly arise from the edges. Now this whole process is wire bonding of semiconductors. Sometimes things can go south, and you might end up facing two issues while doing wire bonding.
- The electrical conductance can be too low during the process
- Less number of wires used for each chip
Now poor electrical conductance eventually disrupts the performance of high-frequency devices, and insufficient wires hamper the data transmission of the chips as well.
People started to find portable semiconductors and circuits not appropriate as their wires were thin and too long, which increased the power losses and lagging.
Now this led to the invention of flip chip packaging, which was a one-stop solution to major problems that occur during wire bonding. The flip-chip method made the manufacturers use bumps instead of wires for the purpose of connections.
You place these on top of the wafer, which increases the electrical density throughout your setup. After this, you cut the wafer and flip the chips to combine them with the substrate by using special copper pillars.
WLP is the simplest technique that most producers rely on today. Major giants in the semiconductor industry use WLP to ensure positive results.
Types of WLCSP: Wafer Level Chip Scale Packaging
WLP has two major divisions. These are fan-in and fan-out types. The interposer is the main factor that differentiates these two types on the whole. For the fan-in type, you keep the sizes of the die and interposer the same.
For the fan-out type, the interpose is always bigger than the die. These processes are also different from a standard WLP package because you apply the interposer on these types directly, which does not happen in the WLP. You can even cover the die and interposer for these two types to protect them under stressful and non-favorable conditions.
Benefits of WLCSP: Wafer Level Chip Scale Packaging
There are certain benefits of using the fan-out method in different applications.
- It is reliable for producing TSVs that are silicon-made wires. These are highly cost-efficient and save enough energy when there is a need to achieve more electrical density.
- TSVs shrink the packages and make them slimmer without their quality at all.
Purpose of WLCSP: Wafer Level Chip Scale Packaging
- The main purpose of using the fan-out method is to draw out the same features of chips, even on artificial wafers. Such wafers use polymers that are affordable for production processes.
- Another purpose is to expand the space between the individual chips and their connections.
Sub-categories of WLCSP: Wafer Level Chip Scale Packaging
You can carry out fan-out WLP in two different ways; let’s check them out below:
Chip-First:
- In this way, you need to incorporate the chips into a fine metallic entity.
- Now the next step is to perform the RDL as per its standards and guidelines.
- Chip’s first method is reliable due to its cost-effectiveness.
- Not only is its affordability attractive for the producers, but it also offers excellent performance in I/O devices and operations.
Drawbacks of Chip First:
Despite the fact that the chip-first method is viable, there are some problems that might occur. It can lead to faults like die shift, die protrusion, and wafer warpage.
Chip-Last (RDL-First):
- In this process, you need to develop the RDL in the first place.
- Now, once the RDL is formed, place it on the wafer.
- After this, it’s time to develop the chips for melding them during the packaging procedure.
- Molding is important before you place the chips on RDL.
- The purpose of molding is to prevent the wafer warpage as much as possible.
- It is exceptional in electrical conductance and has an impressive pitch scale for your ease.
Drawbacks of Chip last:
- If you talk about the reliability of this process, it does not meet some of the industry standards that make it doubtful for usage.
- It also offers much less TSV potential as compared to Chip-first.
Uses of WLCSP: Wafer Level Chip Scale Packaging
Uses of WLCSP:
- One major use of WLP is in I/O devices, as this industry is growing at a rapid pace. The industry stands only on fine interconnect density, and for that, there is nothing more reliable than WLP itself. WLP and RDL come together to offer durability and a certain boost to interconnect density for I/O applications.
- RDL is beneficial for the WLP process because it allows different chips to have exceptional features which will be later used in several applications. The encapsulations offered by RDL are useful for developing smartphones and other forms of semiconductors.
Advantages of WLCSP:
- WLP allows you to place chips on chips in vertical and horizontal positions
- Due to the flexibility offered by WLP, different variants of ICs are now common.
- The ICs developed from WLP are useful for finetuning the fan-out technology and sustaining TSVs when you use them for high-density areas.
- WLP is also reliable for increasing the bandwidth of your system.
- WLP consumes less power as well.
- It is important for developing image sensors, AI devices, and IoT smart home appliances.
