Speeding up the Design Cycle: 10 Things to Remember


Reading time ( words)

Many people understand the value of a PCB, but do not understand the best way to interact with PCB manufacturers. Poor planning and communication with fabricators slows down the design cycle and increases overall costs for your project. 

In this column, I will attempt to help streamline the design cycle through fabrication. Following my tips will minimize the need for future revisions and ensure you get quality boards on time.

10. Eliminate Conflicting Information

It is essential that you eliminate any conflicting information from your drawings or read-me files. Make sure that all documentation is the same. If one document says half-ounce and another says one-ounce copper, you may expect a call asking which it is to be. If you need the part expedited, remember that this takes valuable time away from the build and from you getting your part.

9. Provide an IPC Netlist

An IPC netlist will allow the fabricator to check your design against your exported data. Make sure any known or intentional netlist mismatches are noted again so your CAM group does not waste time calling you to check on things you are already aware of.

Be careful with castellated pads where plated half-holes at the board’s edge will make a connection to a post at some point after fabrication. These typically come up as “broken” or open nets because when the bare boards are fabricated, no post exists to connect these castellations.

Known A-gnd to D-gnd shorts should also be noted. Make sure no non-plated holes have been specified as test points on the IPC netlist. If you are specifying net-compare on your documentation, be sure to include it!

8. Check for Discrepancies on NC Drill File

Double-check to ensure there are no discrepancies of count, size or plating status on the NC drill file. Either one of these can cause communication delays. 

7. Communicate With Your Fabricator ASAP

In order to facilitate the best communication, you need to meet with your chosen fabricator as soon as possible in the design cycle. Check with them for validation of any impedance you may have. Make sure these notes do not conflict either.

Be sure to: Check for proper reference planes. Make sure impedance traces do not traverse multiple splits or lack ref-planes altogether. Differentiate between single-ended and differential type structures by a tenth or a hundredth of a mil. Again, fabricators cannot resolve these small increments, but this allows the fabricator to uniquely select just the impedance tracks for any resizing that may be necessary to meet desired impedances.

Make sure the space between differential pairs is consistent throughout the run. Allow for process deviation, setting up a part as .1 mm trace and space on half-ounce starting copper does not leave room for any trace resizing that may be necessary to meet the impedances if dielectric cannot be altered.

When calling out materials, call out the 4101/# such as 4101/126. This will allow the fabricator to use any material that falls within the /126 criteria. Calling out a specific material may limit the pool of fabricators that can build the board. Avoid creating same net spacing violations when terminating differential pairs, and do not “wrap” the differential pairs around the terminus.

To read this entire column, which appeared in the October 2015 issue of The PCB Design Magazine, click here.

Share

Print


Suggested Items

TTM’s Approach to Stackup Design: Train the Customer

01/12/2021 | I-Connect007 Editorial Team
In this interview with the I-Connect007 Editorial Team, TTM’s Julie Ellis and Richard Dang drill down into stackup design, detailing some of the common stackup challenges that their customers face when designing for both prototype and volume levels, and offering advice to designers or engineers who are struggling with stackup issues. They also discuss why having too many different prepregs in a stackup can be asking for trouble, and how proper stackup design can optimize both the fabrication and assembly processes.

Chapter 1 Excerpt from the Book ‘Thermal Management: A Fabricator's Perspective’

12/08/2020 | Anaya Vardya, American Standard Circuits
Heat cannot be efficiently exchanged with stagnant air surrounding a hot device; however, it can be transferred away from the electronic component to the PCB using thermal vias. A thermal via is a good conductor of heat that runs between the top layer and bottom layer of the PCB, dissipating heat through simple conduction. In simple terms, thermal vias are plated holes located under, or electrically connected to, a surface-mounted heat source on a PCB that allows heat transfer through the hole.

This Month in Design007 Magazine: HDI Design, Landless Vias, VeCS, and More

11/09/2020 | I-Connect007 Editorial Team
Andy Shaughnessy, Happy Holden, and Dan Feinberg recently met with James Hofer, general manager of Accurate Circuit Engineering, to discuss via design techniques and via reliability from the fabricator’s viewpoint. As Hofer explained, even with open lines of communication between the designer and the board shop, there are plenty of variables to contend with regarding proper via design, especially when working with PTFE materials.



Copyright © 2021 I-Connect007. All rights reserved.