A customer had a question on the AD8222. A number of parts had shown offset and gain fluctuations over normal operating temperature, placing them out of specification. The customer asked whether the "plastic glass transition temperature" of 130°C requires a new soldering profile to avoid damage, as compared to the standard LFCSP profile shown in AN-772.
Also, no stock was seen for "no thermal pad" version (H option). The customer wanted to verify this variation was currently offered.
You should be able to use the standard soldering profile. The "plastic glass transition temperature" should really just be called "max junction temperature" in this datasheet, and only applies to continuous operation.
We recently got the ability to manufacture the LFCSP package without the thermal pad. The AD8222 dual in amp is now released in this package. You can order it and it should arrive with whatever the lead time currently is. Because we released this package version for the AD8222 recently, its volumes are small compared to the "thermal pad" version. The "thermal pad" option was the only package we had available when we first released the AD8222 about 4 years ago, and therefore has quite a bit more volume, since it is what our customers have designed in over the past few years. Therefore it is more likely that there will be stock of the thermal pad part available. Since the performance of the "no thermal pad" option should be better, in the future we expect more engineers to design in this part than the original "thermal pad" package. So we expect the "no thermal pad" volume to eventually surpass the "thermal pad" option, but it will take a few years.
The "no thermal pad" option offers two main advantages over the "thermad pad" option: 1) It gives you the ability to route underneath the package. 2)It is much more robust to solder flux residue. If the cleaning step in the manufacturing process is not well controlled, solder flux residue can create resistive paths underneath the part. Since the thermal pad is tied to the supply voltage, a resistive path between it and the input pin can increase apparent bias currents/lower input resistance.
This same discussion also applies to the AD8224.
To our knowledge, (please comment if you have seen it elsewhere), we are the only manufacturer that provides a 16 lead LFCSP without the thermal pad. We feel it gives us a competitive advantage in low power parts like the AD8222/4 where bias current and careful layout is important. We currently use this package with the AD8220, AD8224, and AD8295 and expect to use it for more parts in the future.