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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Quality is found in the design as well as the process.

Solder defects are inevitable. Reducing their risk is mandatory, especially if you’re aiming to make money as a result of operations. Machines are certainly not “almost human,” but they do go through seasonal changes and have moods. Without proper upkeep, they fall into disrepair. The goal in assembly is to dial in the thermal profile of the soldering equipment to minimize solder defects.

Footprint model accuracy is an enabler, but that work can be undone by improper routing and copper-flooding techniques. Placement too near the edge of the board where the temperature fluctuates to a greater degree can decrease yields through the soldering process. Tombstoning is one thing to watch for, but other dangers are present on the frontier.

The Goldilocks zone. Another defect can occur when one lead of a component is close to the edge while the other is farther inward. Wirewound resistors and inductors can become open circuits or more insidiously latent defects, where the wire pulls away from the lead only when there is a temperature rise or a mechanical shock to the system. Ceramic caps can actually crack when one lead solidifies before the other one.

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