Assign the Exposed Thermal Pad to Its Specified Electrical Net

An exposed pad beneath a package may carry an electrical node as well as heat. Automatically connecting it to ground can therefore create a functional error or a short. Read the exact package pin definition before designing its copper area and thermal-via connection.

Find the pad in the pinout

Analog Devices’ LT3080 datasheet identifies the exposed pad as OUT for specified packages and requires it to be soldered to the PCB. This is a concrete counterexample to assuming that every thermal pad is ground. Other devices and packages have their own requirements.

Record the exact ordering code, package, exposed-pad number and required connection. Check pin descriptions, package notes and layout guidance together. If the documentation is ambiguous, resolve the connection with the manufacturer rather than guessing from a reference image.

Make the connection visible in CAD

Ensure the schematic symbol and footprint include the exposed pad with the correct pin mapping. Verify its assigned net in the board database. A hidden or unnumbered thermal feature can escape ordinary schematic review while becoming connected by a copper pour.

Follow thermal vias through every connected layer. Confirm that the copper used for spreading heat belongs to the required electrical node. A via that improves heat flow also creates an electrical connection, and a buried plane with the wrong net is not an acceptable thermal shortcut.

Review nearby conductive structures

Check clearance to mounting hardware, heat spreaders, shields and test fixtures. If the thermal path reaches a metal part through an interface material, establish whether electrical isolation is required and how it is verified. Thermal conductivity alone does not establish that requirement.

Also review the effect of enlarging a switching or sensitive node when the exposed pad belongs to one. The appropriate copper geometry must satisfy the device’s electrical and thermal guidance together. More copper is not a universal instruction independent of the node function.

Verify before assembly and substitution

Use connectivity checks and a focused layout review to confirm the pad net before fabrication. During bring-up, investigate unexpected continuity at the exposed-pad network before applying power. Keep any intended connection to a chassis or fixture documented in the test setup.

When substituting a device or package, compare exposed-pad function explicitly even if the perimeter pins appear compatible. Retain the datasheet reference and CAD mapping with the review. This makes the pad a visible circuit element and prevents a mechanically familiar package from inheriting an electrical connection that belongs to another component.