Mechanical Through-Hole Connection: How Copper Rivets Connect Double-Sided PCBs
A double-sided PCB has copper structures on both sides of the substrate. Wherever an electrical connection is required between these layers, simply drilling a hole is not enough. The two copper layers must also be electrically connected.
In industrial PCB manufacturing this is commonly achieved using plated through-holes. For in-house PCB prototyping, however, mechanical through-hole connection with small copper rivets provides another practical method for connecting the two sides of a double-sided PCB.
In Brief
Mechanical through-hole connection uses a small conductive rivet inserted into a drilled PCB hole. The rivet passes through the substrate and is mechanically formed using a corresponding riveting tool.
Unlike conventional electroplating, the process does not deposit a conductive layer onto the wall of the drilled hole. Instead, the rivet itself forms the physical connection through the board.
Why Double-Sided PCBs Need Through-Hole Connections
On a double-sided PCB, traces can be routed on both the top and bottom copper layers. The insulating PCB substrate separates these layers, so they are not electrically connected simply because a hole passes through the board.
When a signal, power connection or ground connection needs to move from one side of the PCB to the other, a conductive path through the board is required.
Top Copper Layer
Carries traces and pads on one side of the PCB.
PCB Substrate
Mechanically supports the board but electrically separates the two copper layers.
Bottom Copper Layer
Provides additional routing space on the opposite side of the PCB.
What Is a Plated Through-Hole?
In conventional PCB production, a plated through-hole (PTH) contains conductive material along the wall of the drilled hole. This conductive layer connects copper features on different sides or layers of the PCB.
Industrial PCB manufacturing commonly creates this conductive connection using chemical and electrochemical processes that deposit copper inside the drilled holes.
What Is Mechanical Through-Hole Connection?
Mechanical through-hole connection approaches the same electrical requirement differently.
Instead of depositing copper onto the wall of the hole, a small conductive rivet is inserted through a correctly sized drilled hole. The rivet extends through the PCB substrate and is then mechanically formed using a riveting tool.
Copper rivets are therefore often used as vias when producing double-sided PCB prototypes in a laboratory or in-house prototyping environment.
Mechanical Riveting vs. Conventional Through-Hole Plating
Conventional Plated Through-Hole
Conductive material is deposited onto the internal wall of the drilled hole.
This approach is standard in industrial PCB manufacturing and can also be implemented in laboratory environments using dedicated through-hole plating processes.
Mechanical Through-Hole Connection
A conductive rivet is inserted through the drilled hole and mechanically formed against the PCB.
The connection is created using the rivet rather than by depositing a conductive layer onto the wall of the hole.
Terminology
Mechanical riveting is often grouped with through-hole plating equipment because it solves the same practical requirement: creating electrical connections between PCB layers.
Technically, however, the process is different from chemical or electroplated through-hole production because the wall of the drilled hole itself is not plated.
How Mechanical Through-Hole Riveting Works
The exact procedure depends on the riveting system being used, but the fundamental process is straightforward.
Design
Define the required layer connections and appropriate holes in the PCB design.
Drill
Drill the PCB using the hole diameter specified for the selected rivet.
Insert
Place the copper rivet through the prepared PCB hole.
Select the Tool
Use the riveting tool corresponding to the selected rivet diameter.
Form the Rivet
Apply controlled mechanical pressure to form the rivet against the PCB.
Inspect
Inspect the completed connection and verify the board according to your normal prototype testing procedure.
Why Rivet and Drill Diameter Matter
The PCB hole, copper rivet and riveting tool form a matched mechanical system. The drill diameter must provide the correct hole for the selected rivet, while the forming tool must correspond to the rivet diameter.
Using the dimensions specified for the particular riveting system is therefore important. Rivet dimensions and recommended drill sizes are not universal between all manufacturers and systems.
Do Not Assume a Universal Drill Size
Rivets from different systems can have different internal, external and collar dimensions. Always use the drill diameter and riveting tool specified for the particular rivet being used.
MIPEC Rivet and Drill Diameters
The MIPEC FAVORIT system supports six copper rivet sizes. Each rivet diameter is matched with a defined PCB drill diameter and corresponding FAVORIT riveting tool.
| Rivet diameter | Drill diameter |
|---|---|
| 0.4 mm | 0.6 mm |
| 0.6 mm | 0.8 mm |
| 0.8 mm | 1.0 mm |
| 1.0 mm | 1.5 mm |
| 1.2 mm | 1.7 mm |
| 1.5 mm | 2.0 mm |
PCB Design Considerations for Copper Rivets
Mechanical through-hole connection should be considered during PCB design rather than only after the board has been machined.
The designer needs to account for the required drill diameter and the physical space occupied by the rivet around the hole. This becomes particularly important when vias are positioned close to traces, pads or other board features.
The selected rivet must also provide sufficient internal clearance if a component lead or connector pin is intended to pass through the rivet.
When Does Mechanical Riveting Make Sense?
Mechanical riveting is particularly useful for in-house double-sided PCB prototyping where a laboratory needs a practical method of creating layer connections without introducing a chemical or galvanic through-hole plating process.
Double-Sided Prototypes
Creates connections between the top and bottom copper layers of prototype PCBs.
In-House Fabrication
Fits naturally into laboratory PCB milling and drilling workflows.
Mechanical Process
Creates the layer connection without a chemical or electroplating bath.
Limitations of Mechanical Riveting
Mechanical riveting is not a universal replacement for industrial plated-through-hole production.
Every rivet must be physically inserted and formed, which adds a manual operation for each through-hole connection. The rivet also occupies physical space on the PCB, so the required hole and pad geometry must be considered during layout.
For prototypes requiring a very large number of layer connections, very dense geometries or more complex multilayer structures, other through-hole connection technologies may be more appropriate.
Mechanical Through-Hole Connection in the MIPEC Workflow
In the MIPEC PCB prototyping workflow, mechanical through-hole connection follows PCB milling and drilling.
The FAVORIT manual press is used together with diameter-specific riveting tools and matching copper rivets. The required tool and rivet size are selected according to the PCB design and drill diameter.
Sources & Further Reading
- MIT Center for Bits and Atoms – PCB Rivets: practical use of copper rivets as vias in double-sided laboratory-fabricated PCBs.
- Vanderbilt University – PCB Manufacturing, Rivets: use of rivets for through-hole connections between copper pads on opposite sides of a PCB.
- LPKF – Through-Hole Plating Systems / Rapid PCB Prototyping TechGuide: overview of riveting, conductive-paste and electroplating approaches for through-hole connections.
Technical Note
Rivet dimensions, drill diameters and processing procedures vary between through-hole connection systems. Always follow the specifications applicable to the equipment and rivets being used.