One afternoon, I received a project from a client who needed to add components to an existing PCB. The timeline was set for 3 days, and the client, who had no technical background, naively assumed that his project was very simple… 1. Cognitive Bias: Adding Components Equals Minor Modifications The client’s insistence on a “tight schedule” often stems from an underestimation of the complexity involved in PCB revisions. They simplistically equate “adding components” with “drawing a few lines and adjusting positions,” while overlooking the hidden technical adjustments required. This is manifested in:
Ignoring the “Layout Chain Reaction”
Adding new components may require adjustments to the positions of existing components (such as avoiding space and optimizing heat dissipation), leading to the potential disruption of critical signal routing (such as high-speed differential pairs and clock lines), necessitating a complete rerouting to meet timing requirements;
Changes to the power/ground plane segmentation may require a redesign of the stacking structure (such as adding ground plane isolation) to avoid power noise;
Adjustments to the position of connectors or interfaces may lead to interference with the enclosure/structure (such as window positions and mounting hole locations), requiring re-coordination with structural design.
The client may think, “It’s just adding an LED or capacitor,” but in reality, it could trigger a layout reconstruction that affects the entire design. This is a common issue among all users: “My PCB is just adding a component; why is it so complicated and time-consuming?”
2. Simplified Judgments on Routing Complexity
The type of new components (such as high-speed ICs or RF modules) can directly impact routing difficulty;
If a high-speed ADC chip is added, strict control of differential pair spacing and impedance matching (e.g., 100Ω±10%) is required, which may necessitate adjustments to existing routing rules (such as trace width and spacing);
If a high-current power module is added, power traces may need to be thickened (e.g., from 0.5mm to 1mm) or the number of vias increased, which could lead to the copper thickness/routing density of the power layer exceeding the factory’s process capabilities;
If sensitive signals (such as sensor analog signals) are added, a shielding ground plane or isolation slot may need to be introduced to avoid crosstalk with digital signals.
If the client lacks a technical background, they may not recognize these “implicit adjustments” and only focus on whether the components are placed correctly.
In summary: Be cautious when accepting urgent orders! If the client has no understanding of the technical aspects, it is best to pass on the project! Choose wisely and filter qualified clients!