The top solder layer in Altium refers to the top soldermask layer. It's important to understand that this layer is a negative image of where you don't want solder mask, and where you want exposed copper for soldering.
Understanding the Top Solder Layer
The Top Solder layer in Altium isn't the actual copper pad layer. Instead, it's the layer that defines the soldermask on the top side of your PCB. Here's how to visualize it:
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Soldermask: This is a protective layer, typically a thin, green material, that covers most of the copper on a printed circuit board (PCB). It prevents solder from sticking to areas you don't want it to, thereby preventing shorts during soldering.
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Negative Layer: The key concept is that the soldermask layer is a negative image. This means:
- Violet areas in the Altium viewer indicate no soldermask is present. These are where the copper will be exposed for soldering.
- Empty areas mean the area is covered in soldermask.
Table Summary
| Layer | Type | Meaning | Color (Typical Altium) |
|---|---|---|---|
| Top Layer | Positive | Copper traces and pads (where you want copper) | Red |
| Top Solder | Negative | Soldermask (where copper is not masked) | Violet (no soldermask) Empty (soldermask) |
Practical Implications
- Exposing Pads: To expose copper pads for soldering, you create violet areas on the top solder layer that overlap the pads on your Top Layer. This tells the PCB manufacturer to remove the soldermask from these locations.
- Preventing Solder Bridges: The soldermask is used to prevent solder from flowing where it shouldn't, reducing the risk of short circuits during soldering, especially around closely-spaced pads.
- Understanding Gerber Files: When you generate Gerber files for manufacturing, the top solder layer will be output as a negative image. PCB manufacturers interpret this to properly apply the soldermask to your PCB.
Example
Consider a standard surface mount component. The component's pads would be defined on the Top Layer (red), and the soldermask openings for these pads would be defined on the Top Solder layer (violet for no soldermask). The area around the pads, which is not designed to be soldered, will be filled with soldermask and appear empty in the top solder layer view.
