The Essential Differences Between Storage Modules and Embedded Chips

Here, we want to explain the differences from the perspective of an external module (such as TF cards) and embedded chips (like SD NAND or eMMC, which can be soldered directly onto the PCB).

For those reading this article, take a moment to look around and you might notice that there are many manufacturers making TF cards. From large brands in the U.S., Japan, and Korea to smaller white-label manufacturers around Shenzhen, everyone seems to be in the TF card business. However, when it comes to embedded eMMC or eMMC-brand manufacturers, there are very few. Why is this the case?

From a simple chip architecture perspective, TF cards, SD NAND, and eMMC all consist of NAND Flash wafers, a NAND Flash controller, and firmware.

However, there are significant differences in the original product positioning. Storage modules (such as TF cards) are designed as external storage products. They can be easily inserted or removed, and replaced at any time without the need for high-temperature reflow soldering. On the other hand, embedded chips, such as SD NAND and eMMC, are designed as embedded storage. They are soldered directly onto the PCB and replacing them is more complicated, requiring the product to be disassembled and specialized tools for rework. Additionally, embedded chips must be able to withstand temperatures of around 250°C, as the chips need to go through high-temperature reflow soldering when mounted onto the PCB.

What are the differences due to this distinction in positioning?

1. Different Requirements for Defect Rates:

• For external storage products (like TF cards), if a defect occurs, you simply return the card to the manufacturer and get a replacement. However, if embedded chips like SD NAND or eMMC are defective, the entire product must be returned to the factory. The product will then undergo rework, including disassembly, board cleaning, re-soldering, and finally, sending the repaired product back to the end user. This process is time-consuming and labor-intensive, with significant negative impacts on the user experience and brand reputation. Even a small defect could result in catastrophic consequences.

• Therefore, the requirements for yield rates are vastly different between external storage modules and embedded chips. In the TF card market, it’s not uncommon for suppliers to offer non-warranty trading models (where the 1% defective rate is factored into the price). However, such models are completely unacceptable in the embedded chip market.

2. Different Consistency Requirements:

• For external storage modules like TF cards, as long as the basic transfer protocols are met, there are no stringent requirements for the internal controller or Flash used. However, for embedded chips like SD NAND and eMMC, which store system code or data, the consistency requirements are very strict. Any changes to the internal wafer or controller must be communicated to the end user. Additionally, the product needs to go through re-sampling, testing, and certification. Otherwise, the product may suffer from issues such as mass failures, like the situation where many smartphones become "bricks."

3. Material Quality and Cost Requirements:

• Due to fierce competition (with many manufacturers) and relatively low quality requirements, external storage products like TF cards tend to prioritize cost in their choice of materials. However, for embedded chips like SD NAND and eMMC, the emphasis is on material quality. These materials include the Flash wafers, chip substrates, bonding wires, and black resin. The materials selected for embedded chips are typically of higher quality and differ significantly from those used in external storage products.

4. Different Requirements for Packaging and Testing Processes:

• For embedded chips like SD NAND and eMMC, the production processes such as wire bonding, molding, baking, and cutting require very precise control. Material control is crucial to avoid batch defects. Without proper control over these processes, defects can easily occur.

Understanding Why There Are Many TF Card Manufacturers and Few SD NAND or eMMC Manufacturers

Now, you can understand why there are so many manufacturers of TF cards, while there are relatively few manufacturers of SD NAND or eMMC chips.

Currently, in the market, external storage modules include TF cards, SSDs, USB drives, etc., while embedded chips include SD NAND, eMMC, and eMCP. If you compare the number of manufacturers in each category, you will likely notice a common trend.

Conclusion:

Many customers consider CS Brand SD NAND to be a "surface-mounted TF card," but it is more accurately described as a mini version of eMMC. Compared to eMMC, CS Brand SD NAND is smaller in size, has fewer pins, lower capacity, is easier to solder, and offers better compatibility.