Step PCB | frame technology | exposed inner layers | 3D | printed circuit board | multilayer assembly

Frame and Step Technology are similar yet fundamentally different printed circuit board (PCB) technologies. They form a kind of "2.5D technology," where the typically two-dimensional PCB surfaces are modified with elevations or recesses. The primary difference between frame and step PCBs is whether copper structures are required on the outer layers or if they only exist internally.

Frame Technology

Sandwich Frame PCBs with counter-sink holes and depth milling

In Frame Technology, one or both sides of the PCB are laminated with FR4 parts using 3M adhesive or no-flow prepreg (which is more expensive). These FR4 frames usually provide mechanical protection. In some cases, the cutouts serve as "pockets" for encapsulating mounted components.

Advantages of Frame Technology:

• Cost-effective process
• Possible on both sides, with varying thicknesses
• Special mechanical processes are possible
• Contactable, internal structures
• High-layer count multilayers can be cost-effectively combined with frames

Disadvantages of Frame Technology:

• The outer side of the frame has no copper
• No conductive connection from the outside to the inner layer
• 3M adhesive is less stable than prepreg bonding
• Placement limitations (must be adjacent to the contour)
• Frame edges may show slight resin leakage or minimal resin retraction

Step Technology

Step PCB with exposed inner layers and contactable outer layers

In Step Technology, complete multilayer PCBs are produced using laminate technology. Laminate technology refers to a process where the outer layers are not pressed as foil but are instead complete two-layer cores. However, the areas that will later be exposed are deep-milled from the back of the core and cut out in the prepreg before pressing. After completing the multilayer, these areas are deep-milled so that the unbonded parts can be removed, and the inner layers are exposed.

Advantages of Step Technology:

• Possible to expose on both sides, with varying thicknesses
• Copper structures on both the inside and outside
• Stable prepreg bonding
• Flexible placement of the exposed areas
• Special mechanical processes are possible
• Contactable, internal structures

Disadvantages of Step Technology:

• Complex, expensive process