A. CML supplies a number of devices in VQFN packaging. Due to their compact size, the devices available in these package types are called “Qx” packages, where x is a reference to the number of pins available (e.g. Q1 = 64 pins).

CML advises that special care should be taken when assembling any Qx (e.g. Q1 64 pin VQFN) packages on to a PCB.
In some cases, such as the CMX990 and the CMX998, it is necessary for both electrical and thermal dissipation reasons to attach the central exposed pad to a ground plane on the PCB.

In other cases, unless stated to the contrary, it is not essential for electrical or thermal dissipation reasons to make such connection, however CML would still recommend that this pad be soldered down to the PCB so as to provide good physical attachment. If this is done, the PCB land to which it is attached should be electrically unconnected to other parts of the PCB.

The following link will take the reader to a CML guidance note on using the CML VQFN package. It provides comprehensive guidance for assembling such packages into an application QFN PCB Design Guidance Notes.

A. CML Microcircuits may supply two subtly different QFN/WQFN packages as stated in the datasheet.

With regard to mounting this package (reference to IPC610) solder toe fillets are not required or achievable on the side walls of all QFN/WQFN Packages.

Cross-Section View of an Acceptable Solder Joint on QFN/WQFN Packages with Pull-back Design