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58 DESIGN007 MAGAZINE I JUNE 2023 Ill-fitting parts can frequently cause delays and cost overruns, and undermine PCB per- formance, durability, and overall quality of the board. ese poor results can be avoided. Here are five methods designers can implement to avoid common, parts-related manufacturabil- ity pitfalls. 1. Pay close attention to pinhole size It's important to check component physical dimensions, consider dimension tolerances, and account for variation that can affect fit. Pins can be the wrong size or have the wrong spacing, and components can be much larger than their footprint or land pattern might indicate. Alternate or replacement components can be on the wrong end of the tolerance range. It just takes a few mils before things don't fit and assembly starts to go wrong. Finding a good alternate part can be a challenge, which is why datasheets are invaluable. In addition to watching part sizes, pay close attention to the minimum, nominal, and maxi- mum material conditions for the original part. 2. Use the product datasheet when designing the land pattern One of the most frustrating mismatches with alternate through-hole parts is when the land pattern matches, but the pin size is off. If hole sizes are too tight, pins may not fit through the holes. Or, if pins do go into the holes, they may not solder well. Solder will need to flow up through the gap between the pin and the hole barrel. If there is not enough space to allow solder mass to flow through the hole, the circuit board will absorb heat from the molten solder and cause the solder to solidify part way up the hole. is "cold" solder joint can result in premature failure of your circuit. When designing the land pattern, the pin size and tolerance range for com- ponents can be found in the product datasheet. Use that information to plan the proper hole size. Com- ponent holes should be sized correctly t o a l l o w Avoiding Five Common Pitfalls of Parts Connect the Dots Feature Column by Matt Stevenson, SUNSTONE CIRCUITS

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