diff --git a/tech/PCB.wiki b/tech/PCB.wiki
index 4245eb4..b2744e7 100644
--- a/tech/PCB.wiki
+++ b/tech/PCB.wiki
@@ -9,6 +9,8 @@ help you turn breadboard circuts into PCBs.
 == Structure ==
 
 * Components are connected with copper trace (wire)
+* PCB is several layers 
+  - Inner layers are usually GND or VCC
 
 == Software ==