Stop in for a cup of coffee
Getting further into the dig. I have discovered that the smaller components are almost entirely encased in the insulating RTV and only the larger ones are in half of each.
I took two similar sized pieces of each layer and allowed them to equilibrate to a fixed temperature heat plate at about 125*. The RTV warmed up quicker (insulator) and the silica mix layer got hotter (higher heat capacity). The RTV layer was only half as warm as the silica layer.
When both were placed on the room temperature aluminum heat sink plate, they both cooled down at about the same rate but the silica layer got cooler a little quicker.
This means the silica layer has higher heat capacity (holds more heat) but sheds it faster than the RTV layer (higher heat conduction). This results in a more extreme thermal cycle taxing the components.
This is a bad combination for a circuit board. The smaller components are encased in an isulating layer that won’t let them shed heat and the larger components are encased in half that and half in a layer that holds more heat before it sheds it. Add to that the external aluminum heat sink is at the opposite end of the case from where the heat is being generated making it useless.
No wonder these things fry quickly.
Getting further into the dig. I have discovered that the smaller components are almost entirely encased in the insulating RTV and only the larger ones are in half of each.
I took two similar sized pieces of each layer and allowed them to equilibrate to a fixed temperature heat plate at about 125*. The RTV warmed up quicker (insulator) and the silica mix layer got hotter (higher heat capacity). The RTV layer was only half as warm as the silica layer.
When both were placed on the room temperature aluminum heat sink plate, they both cooled down at about the same rate but the silica layer got cooler a little quicker.
This means the silica layer has higher heat capacity (holds more heat) but sheds it faster than the RTV layer (higher heat conduction). This results in a more extreme thermal cycle taxing the components.
This is a bad combination for a circuit board. The smaller components are encased in an isulating layer that won’t let them shed heat and the larger components are encased in half that and half in a layer that holds more heat before it sheds it. Add to that the external aluminum heat sink is at the opposite end of the case from where the heat is being generated making it useless.
No wonder these things fry quickly.