How Engineers Fit a BLE Data Logger Inside a 2.4 mm Card

Designing a Bluetooth Low Energy logging card at just 2.4 mm thickness requires resolving a fundamental space conflict before any electronics decisions are made. Stacking a coin cell on top of the PCB in the conventional way immediately exceeds the 2.4 mm budget, so the cell is instead recessed into a window cut through the board, making total thickness equal to cell height plus two shell walls. This approach yields a nominal 2.20 mm stack, leaving only 0.20 mm to absorb tolerances, contacts, and bonding layers — with no room to treat any of it as true margin. A sealed, seamless enclosure rules out a battery door or external test points, meaning data readout must be wireless and a single cell must last the device's full service life. Component placement is further constrained by the antenna keep-out zone, which forces the coin-cell window and the 2.4 GHz PCB monopole to occupy opposite short edges of the board.