I and my friend have designed a 0.8mm 4 layer PCB for our project. The top and bottom layers are for signal traces and the middle layers for power and ground. All the components that we use are SMD type and also we have few components on the board which contain plastic.
We did some experiments on soldering the components to the board and have failed a few times. The solder paste which we are using is lead-free solder which melts at 217 degrees celsius. Every component which we are using has a max peak reflow temperature of 260 degrees celsius.
The first time we tried to solder the components we used our hot air soldering station at 260 degrees celsius but we weren't able to solder the components at all, the solder paste wasn't melting. Then we tried higher temperatures, but the stone plate(where we had our PCB placed) seemed to absorb the heat and the board was losing temperature quite quickly.
Then we did some research and saw articles where people were using more than 300 degrees celsius, sometimes 350 and even 370. When we tried these temperatures the soldering was kind of successful, the solder paste melted and everything was soldered correctly. But the plastic components, buttons and the connector, have melted... Which weren't melting at 260 degrees celsius.
Also, we tried soldering some components on 2 layered PCB and everything was soldered within seconds even at 260 degrees celsius. We think that means that our PCB has way more thermal mass because it has 4 layers and also entire ground plane connected to every layer via many vias.
The last thing that's left is preheating the board evenly, so 260 degrees celsius would be enough. We don't have a hotplate, nor infrared heating bed. Considering our board properties and that the hot air soldering station is the only tool, can you guys give us some tips on how to preheat the board, what temperatures to use for preheating and soldering, and maybe which nozzles are better for such purposes?
Thanks in advance!