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14 The PCB Design Magazine • March 2016 what thresholds they desire and where they will reside within the stack, soliciting a quote from a fabricator prematurely may make the quote in- valid. Consult with your assembler for feedback on any panelization aspects to avoid having to reCAM a panel to add or modify based on assy needs. Lastly, do a thourough product review prior to releasing the fab data to avoid lost time due to incomplete or conflicting notes. 3. IPC Netlists, Their Function, and Typical Net-Compare errors What is the purpose of the netlist compare? This method is used to compare your design info against your exported Gerber/image data. This is done prior to any fabrication edits. Required by Class 3 6012, an IPC netlist contains your design info. You may have heard me say this before, but I have been asked by so many of our customers to CREATE an IPC netlist for a class 3 6012 job if they cannot provide one. This defeats the purpose of the net compare in the first place. Because the idea is to check the customer's design against the customer's exported data, creating a netlist from that data would never catch an actual design-to-export data mismatch. What are some things you can check for to minimize time lost for IPC netlist issues? A. AGND to DGND shorts. You may have an analog ground to digital ground short built into the design. You will want to specify that it is a known or expected short, or you may receive a phone call from your fabricator. B. Castellated holes (plated half holes at a part edge) practically scream that they will make a connection to a metal grounding post sometime later in life. They come up as "bro- ken" nets frequently when running an IPC netlist compare. They show up as broken only because at the time of bare board fabrication, they dis not make connection to the posts. C. Surface mounts defined as net points, Likewise, sometimes when a surface mount is defined as a netpoint, we can also come up with erroneous broken or open nets. Again, the netlist may think they are to be connected, but they are only connected after assembly. 2. Check Your Edges For scored parts, do not pour metal any clos- er to the part edge than .015" for an .062" thick part and at least .009" for an .031" thick part. 1. Get Accurate, Timely Quotes How do I make sure I get an accurate quote? It's easy. Don't leave anything out. Don't leave anything open for interpretation. Don't provide a preliminary drawing that you KNOW will change. If the prelim drawing indicates you will have 1,000 vias of a specific size and the final data comes in as 10,000 vias, your price will change. If you have negotiated impedances and a stack-up over time and the data comes in changed, more time will be involved in revali- dating the impedances. Time = money. If the new board is a revision of an older board and only some constraints have changed, make sure the fabricator knows this so he does not reinvent the wheel for some things they have already covered from a previous rev. This could take additional time and delay the quote. And of course, if you do everything listed in this article, you should end up with accurate, timely quotes. As always, I appreciate your time. If you have any comments or feedback I would love to hear from you. PCBDESIGN Mark Thompson is in engineer- ing support at Prototron Circuits. To read past columns, or to contact Thompson, click here, or phone 425-823-7000, ext. 239. the top 10 Ways designers can increase profits