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Redesigning a printed circuit board is a chore that no one likes. Respins of printed circuit boards cost money, delay the schedule, and just aren’t enjoyable for anyone. Yet, many companies are not taking advantage of available tools that can reduce—and in many cases eliminate—PCB respins. Instead, issues that make the PCB difficult or impossible to manufacture are found late in the process, even by the fabricator or assembler. The later in the process, the greater the cost to fix—and it’s not linear.
There are many causes that commonly result in a board that is either impossible to fabricate or assemble, or would produce such a small yield that the cost would be out of range. Whenever this happens, the board must be redesigned to correct the problem before manufacturing can commence.
Often issues are not caught early because of lack of insight to the fabrication/assembly process, and inability to detect the problems visually. A design may appear to meet specs for trace width, but a particular manufacturer may not be able to maintain a minimal-width trace due to undercutting. This is something that would not normally be in a PCB designer’s realm of knowledge.
The key to avoiding respins is to employ design for manufacturing (DFM) techniques, not just before releasing to manufacturing, but all throughout the product design and creation process. Here are five ways that DFM can help you reduce or even eliminate PCB respins by employing Siemens PCB DFM solutions.
1. Stackup material selection.
Every PCB design begins with a stackup. The top and bottom must be aligned as well as any signal and planes in a multi-layer board. Stackup issues are one of the top reasons that respins are required. With higher and higher edge rates, material selection becomes more critical. The traditional methods of using a spreadsheet to define the stackup has run out of gas for today’s speeds. Siemens’ Z-planner Enterprise lets you select and perform “what ifs” from an extensive library of materials. And, like all PCB DFM tools, it allows collaboration with the fabricator to quickly and reliably ensure that all your stackup specs are properly met.
Figure 1: Watch how easily you can select and optimize material selection with Z-planner Enterprise.
2. Solder validation.
Soldering large BGAs with hundreds of balls requires a precise design. Valor NPI performs DFM checks on both surface mount and through-hole connections. When augmented with the Valor Parts Library (VPL), the tool can identify likely solderability issues with their component footprints that otherwise could not be determined without having to build physical prototypes. Using the lead contact areas defined in VPL, Valor NPI examines the design to see if the minimum requirements are met for proper soldering requirements using toe, heel and side, or periphery, depending on the lead, as defined by IPC-7351B. In addition, Valor NPI analyzes the board for proper spacing between the plated-hole wall and the edge of the through-hole lead so that wave soldering will not have any issues.
Figure 2: See how solder validation can catch potential problems with solderability that would affect product yield and reliability.
3. Find manufacturability trouble spots for rigid-flex designs.
Rigid-flex and flex circuitry introduce a level of manufacturability trouble spots that don’t exist with standard rigid boards. Different materials are used in rigid circuits and the interconnection of the rigid and flexible segments must meet rigid design rules to ensure reliability.
Valor NPI can help ensure that your rigid-flex designs are right-first-time by checking to see whether your design has any areas that could make it more difficult to manufacture.
Figure 3: Valor NPI provides DFM for flex and rigid-flex circuits and their unique manufacturability issues.
4. BOM verification.
You no doubt know how complex the bill of materials for a large PCB design can be. Because of that, there are several possible issues that if overlooked can add expense and time through the old nemesis, respin. Valor NPI executes a set of DFM checks on your BOM to ensure it is correct with no duplication and no errors. BOM verification assures that there are no Refdes mismatches, validates that the quantities match, ensures sufficient solder joints for the chosen components, and performs an alternate part analysis to ensure that all alternate parts will properly fit, despite possible small variations in dimensions.
Figure 4: Watch how Valor NPI ensures that your BOM is correct and all alternate parts fit properly.
5. Assembly DFM.
So, you’ve correctly designed your stackup, checked your solderability and flex trouble spots, and you’ve validated the BOM. You should have eliminated fabrication issues, but how about anything that would affect assembly?
Issues that may cause assembly difficulty are difficult to find manually. A visual inspection just can’t find many of them. So, what you need is both a fabrication and assembly expert. In fact, Valor NPI incorporates information from both your fabricators and assemblers so that it can quickly and effectively analyze your design for assembly. Issues such as components protruding over the edge of the board or components that shadow test points, making them inaccessible, are all identified so that they can be quickly remedied.
Figure 5: Learn how to leverage the knowledge of your fabricators and assemblers into your design using Valor NPI.
Valor NPI can find those nasty little details that can wreak havoc in manufacturing, letting you correct them and save a lot of time and headaches. Learn more about the Valor DFM Family of products by clicking here.
Pat McGoff is the Market Development Manager of Valor NPI, Siemens EDA.