UDP vs COB vs PCB — Which Flash Format Do You Need?
UDP, COB and PCB describe three physical ways of building a USB flash device, and the right one depends on where the storage sits in your product. A PCB drive is a finished removable stick built on a circuit board in a housing. COB (Chip-On-Board) bonds the bare die directly to the board, removing the packaged chip. UDP (USB Disk in Package) goes furthest: a complete USB flash device on a single small module you solder onto your own PCB. If you need removable, take PCB. If you need fixed, thin and tamper-resistant, take UDP.
The three formats
| Format | What it is | Typical use | Thickness | Removable |
|---|---|---|---|---|
| PCB | A finished USB drive built on a circuit board, fitted into a housing | Retail and promotional drives | Set by the housing | Yes |
| COB | Bare die bonded directly to the board, no packaged chip | Cost-sensitive compact builds | Thinner than packaged | Depends on the housing |
| UDP | A complete USB flash device as a single module soldered to your PCB | Fixed internal storage in devices | 1.45 mm (11.3 × 24.8 mm module) | No — soldered on |
How to choose
- The user must be able to remove it → PCB in a housing
- It lives inside the product permanently → UDP
- You are cost-sensitive and space-constrained but still need a packaged assembly → COB
- You have your own housing and assembly line → semi-finished board or UDP, whichever fits your mechanics
What "UDP" does not mean here
In flash memory, UDP means USB Disk in Package. It is not User Datagram Protocol, the network transport protocol. The two share an abbreviation and nothing else — if you arrived here looking for the networking term, this is not it.
Mechanical and capacity reference
The numbers that decide fit are the ones buyers forget to ask for. A PCB drive takes whatever thickness its housing allows; a COB build is thinner than a packaged part but still needs a board and assembly; a UDP module is fixed at 11.3 × 24.8 × 1.45 mm and holds 128 MB to 128GB, soldered to your board. We build UDP modules across that capacity range and supply the mechanical drawing once your clearance is confirmed.
| Format | Footprint | Capacity we build | Field serviceable |
|---|---|---|---|
| PCB | Set by housing | 128 MB – 128GB | Yes — removable |
| COB | Thinner than packaged | 128 MB – 128GB | Depends on housing |
| UDP | 11.3 × 24.8 × 1.45 mm | 128 MB – 128GB | No — soldered |
The mistake to avoid
Do not choose UDP for a product that field technicians are expected to service. The module is soldered on, so replacing it means desoldering — fine for sealed devices, wrong for anything meant to be opened. If serviceability matters, take a PCB drive in a housing instead, even at the cost of thickness. The same logic applies to COB: it is compact and cheap, but it ties the storage permanently into your board, so a field-swap is not on the table.
Not sure which applies to your product?
Send your workload — what writes, how often, at what temperature — and we will propose a configuration with the reasoning. We reply to business enquiries within 1 business day.
Request a quoteFrequently asked questions
Can a UDP module be replaced in the field?
Not without desoldering. That is the point for devices where the storage should not be removable, and a disadvantage where field serviceability matters.
Is COB cheaper than a packaged part?
Usually, because it removes the chip package. It is also more sensitive to process control, which is why the supplier matters more than the format.
What capacity can a UDP module hold?
128MB to 128GB in the module format we produce. See the UDP module product page for the current specification.
Can you supply a drawing?
Yes. Send your mechanical clearance and we will confirm which module fits and provide the drawing.