Simplified yet Intricate: Single-Sided PCB Design

Printed Circuit Boards (PCBs) are crucial electronic components. They act as the support structure for electronic devices and serve as the carrier for electrical connections among electronic components. Since its inception in 1925, the evolution of printed circuit boards has led to increasingly intricate layouts, more layers, and greater complexity. However, even amidst these advancements, the most basic form known as the single-sided PCB is still widely employed in various industrial products like radios, washing machines, and remote controls.

Structure of Single-Sided PCB

Traditional FR4 single-sided PCBs accommodate one side of copper, one side of solder mask, and two sides of silkscreen (depending on customer design). Due to the absence of the electroplating step in the production of single-sided boards, the hole walls of these PCBs lack copper (note: board thicknesses of 0.4 mm, 0.6 mm, 0.8 mm, and 2.0 mm are produced by default as double-sided to maximize utilization of board material. For boards of these thicknesses, through-holes will be plated).

Soldering of Single-Sided PCBs

Given the structure of single-sided PCBs, where only one side contains circuitry, soldering is limited to the exposed pads on that particular side. Depending on the component's structure, this results in two distinct soldering methods:

1. Same-Side Soldering

For components where the main body is on the same side as the circuit, often used for SMT-type component soldering.

2. Opposite-Side Soldering

For components where the main body is on a different side from the circuit, commonly used for through-hole component soldering.

Designing Engineering Files

In practical design, a complete PCB is designed layer by layer.

Taking double-sided boards as an example, patterns designed on the top layer are seen directly (e.g., top layer text appears correctly). Conversely, patterns designed on the bottom layer have a mirroring effect; if text is designed on the bottom layer and it appears upright in the design software, due to the mirroring effect, the text on the actual board will appear reversed (since the physical board is viewed from the opposite side).

The same principle applies to the circuit layer. For single-sided boards, when designing circuitry on the bottom layer, because of the mirroring effect, the actual board needs to be viewed from the front with a backlight to match the bottom layer's circuit design (as shown in the figure below).

Characteristics of Factory Production

In actual production, to avoid burrs and peaks, the mirrored image of the bottom layer's wiring is used for the top layer (mirrored production does not affect the customer's original design structure). This approach ensures that the drill bit first penetrates the copper layer on top. Since the substrate provides support underneath, the copper can be drilled very cleanly. Drilling holes with the copper side facing down would result in numerous burrs and peaks.

Special Note

1. Single-sided aluminum-based boards have a conductive aluminum base layer, making them unsuitable for component soldering (soldering could lead to short circuits).

2. Single-sided aluminum-based boards generally have silkscreen printed on one side, applied to the copper-covered side. Printing Silkscreen on the aluminum-based side is not recommended as it may be difficult to read.

Conclusion

In summary, single-sided PCBs have a straightforward design, but careful attention must be paid to the layer where the circuit is located and where soldering occurs to avoid an unintentionally mirrored design.

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