PTH stands for Plated Through Hole, indicating that the hole is conductive and connected to a layer with copper. This enables electrical connectivity. In contrast, NPTH (Non-Plated Through Hole) refers to holes without copper plating on the inner sides, serving as electrical isolators.
PTH holes are primarily used in circuit boards for two main purposes. One purpose is for soldering traditional DIP (Dual In-line Package) component pins. The diameter of these holes needs to be slightly larger than the diameter of the component’s pins to allow for proper insertion of the part.
Another relatively small type of PTH, commonly known as a via, is used to connect and transition the copper conductor lines between the double or multiple layers of circuit boards. PCBs consist of numerous stacked and interconnected copper conductor layers, each separated by an insulating layer. Consequently, these copper conductor layers cannot be directly interconnected, necessitating the use of vias.
The key characteristic of PTH lies in its manufacturing process, where after drilling, a thin copper layer is applied to the hole walls, rendering them conductive. This process ensures lower connection resistance between component leads and copper traces after PCB assembly, enhancing mechanical stability. Today, the majority of PCBs are double-sided or multi-layered, and most vias are plated. Vias can also be designed with slots, split holes (also known as castellated holes), and are not strictly limited to circular shapes.
**Process Flow of PTH**
**1. Alkaline Degreasing:**
This step removes oil stains, fingerprints, oxides, and dust from the holes on the board surface. It adjusts the pore wall from a negative to a positive charge, facilitating the subsequent adsorption of colloidal palladium. After degreasing, rigorous cleaning according to specified guidelines is crucial, including copper deposition backlight testing.
**2. Micro Etching:**
Micro etching removes oxides from the board surface, roughens it to ensure good adhesion for subsequent copper deposition, and activates the newly exposed copper surface for effective colloidal palladium adsorption.
**3. Pre-Activation:**
This step protects the palladium tank from contamination by the pre-treatment tank solution, thus extending the palladium tank’s lifespan. It includes components similar to the palladium tank, except for palladium chloride, which wets the pore walls effectively, enabling the activation solution to enter the holes timely and sufficiently.
**4. Activation:**
By adjusting the polarity through pre-treatment, this step ensures the positively charged pore walls effectively adsorb sufficient negatively charged colloidal palladium particles. This process guarantees the uniformity, continuity, and density of subsequent copper deposition, highlighting its critical role in achieving high-quality results.
**5. Desmear:**
Desmear removes tin ions surrounding colloidal palladium particles, exposing palladium nuclei for catalyzing the initiation of the chemical copper deposition reaction. The use of fluoroboric acid as a desmear agent is widely favored for its efficacy.
**6. Copper Deposition:**
Initiated by palladium nuclei activation, this self-catalytic chemical reaction precipitates chemical copper. The reaction leverages chemical copper and hydrogen byproducts as catalysts, ensuring continuous deposition. Stirring the tank liquid with normal air aids in converting more soluble divalent copper during the process.
PTH stands as a pivotal process in circuit board manufacturing, where through-hole plating, also known as chemical copper plating, deposits a thin layer of chemical copper onto the non-conductive hole walls created during drilling. This layer serves as the foundation for subsequent copper plating operations.
