UDP vs PCB vs COB: what is the difference between USB flash formats?
These three terms describe how a USB flash device is physically built, and they are often used loosely. COB (Chip-On-Board) refers to bonding the bare silicon die directly to the board instead of soldering a packaged chip — a manufacturing method. PCB refers to a finished flash drive built on a printed circuit board, normally inside a housing and removable. UDP (USB Disk in Package) is a complete USB flash device on a small board with no housing, designed to be soldered permanently into your product. The practical question is usually whether the storage should be removable from your device or fixed inside it.
COB is a method, not a product category
COB means the silicon die is bonded directly onto the board and encapsulated, rather than being packaged first and then soldered. It is used in card and UDP production because it makes the finished device thinner and more resistant to physical shock.
Because COB is a manufacturing method, it appears inside several product categories rather than being one. A microSD card is typically a COB device. So is a UDP.
The formats side by side
The table below uses the specifications we supply. Other suppliers will differ in detail, but the trade-offs are the same.
| Format | Dimensions / weight | Removable? | Typical use |
|---|---|---|---|
| TF card (MicroSD-class) | 15 × 11 × 1 mm, 0.25 g | Yes | Devices with a card slot; field-swappable media |
| UDP module | 11.3 × 24.8 × 1.45 mm, 0.819 g | No — soldered to your PCB | Fixed internal storage; tamper-resistant designs |
| Semi-finished board | 12 × 44 × 4.5 mm, 3.2 g | Depends on your housing | Feeding your own housing or assembly line |
How to choose
Work backwards from the device, not from the price list.
- If an operator or end user must be able to remove and replace the storage, you need a card with a slot.
- If the storage must not be removable — sealed units, remote installations, tamper-sensitive equipment — a UDP soldered onto your board removes that risk class entirely.
- If you already manufacture your own housing or have an assembly line, order the semi-finished board and assemble it yourself rather than paying for a finished drive you would have to open.
- If you need a branded product to hand to a customer, order the finished custom drive with the branding applied.
Interface is specified separately
None of these formats dictates the interface. Both our UDP modules and semi-finished boards are available with USB 2.0 or USB 3.0, and capacity range runs from 128MB to 128GB. Controller selection is a separate decision again, and it is the decision that most affects whether your host enumerates the part reliably.
Sources
Figures quoted on this page are from the published reporting listed above. Where a number is an estimate rather than a published figure, it is described as approximate.
Frequently asked questions
Is UDP a network protocol?
In networking, UDP means User Datagram Protocol, which has nothing to do with flash memory. In this industry UDP means USB Disk in Package — a physical format. The naming collision causes real confusion in search results, which is why we spell it out on every page.
Is a UDP more reliable than a card?
It is more physically secure, because it cannot be removed. Whether it is more reliable over time depends on the silicon grade and controller rather than the format itself.
Can a COB device be repaired?
Generally not at component level — the die is encapsulated on the board. That is a trade-off of the format, and it is one reason UDP designs are used where the storage is expected to last the life of the product rather than be serviced.
Which format should I choose for an industrial device?
For most sealed industrial devices, a soldered UDP is the practical choice. Send us your host interface, capacity requirement and mechanical clearance and we will confirm a specification for design review.
Working on a specification?
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