Issue link: https://iconnect007.uberflip.com/i/1538269
AUGUST 2025 I DESIGN007 MAGAZINE 45 • Start with a block-level diagram • Label all connects with comprehensible net names and avoid using auto-generated names • Lay out the schematic in a manner that clarifies locations • Label the schematic so that the next person working with it will easily understand it • Keep communication lines open, so design- ers can ask for clarification from the engineer if they are uncertain how to proceed. A quick back-and-forth, double-checking their under- standing, could prevent a board failure • Use the design rule check (DRC) tool and do not allow any design with schematic errors or warnings to be built Design for Drilling Efficiency and Accuracy To improve the efficiency of drilling during manufacturing and help cut down on errors that can result in damaged or unusable boards, design- ers can take the following steps: • Group components with like hole sizes together. This requires less drill movement and speeds up the drilling process. • Reduce the variety of through-hole sizes from the PCB design by paying close attention to allowances. This will help reduce the num- ber of tool changes required during manufac- turing. Boards cost less, get built faster, and have less opportunity for error. • There are pluses and minuses if you choose the smallest possible hole sizes during design. Smaller hole sizes can reduce the amount of material that needs to be drilled and removed from the board. However, most small-diameter bits have similar parameters regarding revo- lutions per minute (RPM), feed rate, chip load, and retract rate, so the improved drilling effi- ciency is usually pretty small. Smaller bits are more prone to deflection by the glass fibers in the laminate material, can create aspect ratio issues during plating when the board thick- ness to drill diameter ratio is too high, and may impact overall hole quality. • Make sure there is enough space between holes to ensure the structural integrity of the board and avoid drill bit deflection during manufacturing. • Pay attention to the allowances for various through-hole requirements. If multiple allow- ance ranges overlap, select a through-hole size that accommodates as many allowances as possible. Manage Solder to Reduce Heat Sink Failures Heat-sink failures are common and can be difficult to detect, especially when the failure rates are low. However, even if the volume of failures is low, those costs quickly run into thousands of dol- lars. Common issues include: • Uncontrollable, unpredictable solder • Solder wicking through vias • Solder movement under large pads To avoid these problems, first, prevent solder from wicking through vias and ending up on the wrong layers of a PCB. Second, prevent solder from moving past its area of application. To achieve this: • Apply solder mask over the landing pad and open circular "islands" for paste application. If the solder will not behave in a large area, break that area into an array of smaller areas. Since solder mask restricts the paste to its area of application, this reduces the amount of solder connecting the chip to the board, increasing the consistency. Circular solder paste apertures release the solder more reli- ably than those with sharp corners, which helps prevent loose solder balls. • Surround the "islands" with small (~12 mil or smaller) vias that are tented and covered with solder mask. Removing the vias from the immediate area being soldered and tenting them prevents any stray solder from wicking down to the other side of the board while still providing good thermal transfer to the pads underneath. Add these vias as close as possible to the islands. The solder mask tenting will block any solder that wicks onto an exposed via due to manufacturing tolerances. We recommend designers include this as part of their package definition, uniformly applying it to all similar parts in the design. 3 2 C O N N ECT T H E D OTS