[![enter image description here](https://i.stack.imgur.com/ZjmJi.png)](https://i.stack.imgur.com/ZjmJi.png)

For my latest product, I have designed a USB ESP8266 dev kit for hobbyists (<http://rxtx.weebly.com>). The theory is that it fits into a USB-A plug directly through the PCB - hence why I am gold plating the traces. 

But I noticed in several other posts that the PCB needs to be at least 2.0mm thick, but PCB houses charge a lot for that thickness - thus why I am sticking to 1.6mm. To compensate for this 0.4mm thickness, what kind of shim would I need - I only need it to cover an area of 10mm by 8mm and it won't be in contact with any rails - plastic, but which kind? Where could I source it cheaply?

The PCB material is FR-4 (ShengYi Tg140). Also, can you advise me on what glue type to use as I am new to adhesives?

Thanks in advance!