Printed Circuit Design & Fab Online Magazine - Current Issue

Designer’s Notebook

John Burkhert

Make every chip a layout unto itself.

Being a printed circuit board designer is not easy. Parts we used to take for granted have become really hard to come by. Geopolitical trade wars and a pandemic were serious triggers for the undersupply. We really didn’t need a Japanese chip factory to burn down to make things worse. A giant cargo hauler clogging up a vital shipping artery for a week was no help either.

The fear, uncertainty and doubt sown into the supply chain put the squeeze on purchasing managers who, in turn, did their best to secure as much material as possible. Ordering more inventory than their forecasted requirements is a typical kneejerk reaction for the big players. Some purchase orders may be defensive measures, an effort to block competitors that are caught shorthanded themselves.

Automakers are a vital sector of the US, German and Japanese economies. They have been busy lobbying their respective governments to pressure chipmakers, with the goal to create a sufficient supply of devices for the vehicles they want to build. Propping up that industry with their ruggedized devices leaves even less bandwidth for other industries.

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Read more: Is it Time to Design Printed Circuit Boards around the Bill of Materials?

John Burkhert

Getting all the parts and processes aimed in the same direction.

Printed circuit board technology never sleeps. At this very moment, engineering teams are working out ways to increase circuit density with finer-pitch devices. When it comes to placing these components on a PCB, the margin of error shrinks along with the pin pitch. Let’s look at how we can enable these parts on the assembly line.

The first step in mass production of a PCB assembly is preparing the board to take components. The boards may be baked in an oven prior to starting the assembly process. Although they are packed in sealed containers with a little bag of desiccant, the sponge-like dielectric materials still absorb water one molecule at a time. Prebaking releases the steam that could interfere with reflow soldering.

Ideally, all parts on a board will use the same type of technology and will be roughly the same class of components in terms of pin-pitch and other physical aspects (FIGURE 1). Tall and heavy components plus small and light ones are not a good mix. Tall ones create so-called shadows where the surrounding area doesn’t get as hot during soldering.

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Read more: Component Placement is a Game of Compromises

John Burkhert

Raising the topline with good execution will make up for the expense of expediting development.

There is a simple equation when it comes to counting profits. The fixed and overhead costs must be less than the revenue for there to be profit. The first units out of the gate owe the company for all the nonrecurring engineering (NRE) costs. The item will be in the red until all that is paid back by the margin between unit cost and unit price.

In many sectors of the economy, particularly commercial, the cost of goods sold (COGS) is close to the selling price, meaning little margin after overhead is accounted for. (PCB design is among the overhead costs.) Many units must leave the factory and find a consumer before the project hits the breakeven point. Product cycles are such that price erosion puts the squeeze on margins right from the beginning. Consumer hardware is a tough game, no doubt.

Competition among the players keeps us on the path of continuous improvement. Sitting still while others strive to grab your market share actually means moving backward, so let’s take it for granted that we have to keep reinventing our products. Those new features, whatever they are, will likely add to the bill of materials (BoM), which increases the variable costs. We can soften that blow with a few money-saving methods.

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Read more: Money-Saving Tips for Printed Circuit Board Design

John Burkhert

You need a buffer zone.

The truth shall set you free. The truth table of a logic device determines the outcome of a logical operation. A handful of operations are described as gates. The gates are named for the function that applies. To start, two main ones are the AND gate and OR gate. Both usually have two inputs and one output.

You may have a hallway or stairwell light in your home with a light switch at either end. When both switches are in the down position, the light is on. When both are up, the light is also on. If one is up and the other down, the light is off. The truth table for those two switches is shown in TABLE 1.

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Read more: Unpacking Logic as it is Used on a Printed Circuit Board