The Bare (Board) Truth

Column from: Mark Thompson

Mark Thompson has been in the industry for 32 years. He started out in Stockton, California in 1980 as a driller and photo tech right out of high school. He moved to Santa Clara soon thereafter and worked for Multiplex, which became ACI West. In 1993, he relocated to the Pacific Northwest, where he worked for Pacific Circuits, which became TTM, and Praegitzer Industries. He worked with Prototron from 1996–2020 and is now a senior PCB technologist/ Engineering Manager at Out of the Box Manufacturing.

In his free time, Mark is an avid pilot, with a fondness for the aircraft of yesteryear. Mark says, "I have been privileged to fly many biplanes from the 1930s and 1940s, including Fleets, Stearmans, and N3Ns."

May 19, 2021

The Bare (Board) Truth: My Top Six Design Challenges

Narrowing it down to the top six was tough as there are so many challenges for today’s board designers—from incomplete information and footprint generation to power routing constraints. These are just some of my thoughts and is by no means a complete list of all of today’s design challenges.
November 13, 2020

The Bare (Board) Truth: Via Basics

In this month’s column, Mark Thompson addresses what vias are and what they are used for, as well as how they are used in PCB design. He also covers some criteria on pad size vs. via size for fabrication and how vias came about.
September 10, 2020

The Bare (Board) Truth: 5 Questions About Improving Thermal Management

Mark Thompson from Monsoon Solutions answers five questions about thermal management at the design and PCB levels, including how much heat a via dissipates, how to identify potential thermal issues, and more.
September 05, 2019

The Bare (Board) Truth: Teaching the Next Generation—An Overview of Today’s University Courses

In this column, Mark Thompson focuses on the University of Washington, where he counted approximately 163 programs in their catalog of electronics courses. He shares the top 19 courses he thinks are the most valuable for emerging electronic engineers if he were to start his electronics career over again.
June 20, 2019

The Bare (Board) Truth: Fabrication Starts With Solid Design Practices

It’s a fact: Great board design is the key to a great PCB. I’m even more certain of this after spending two days in a wonderful class presented by Rick Hartley titled “Control of Noise, EMI, and Signal Integrity in High-speed Circuits and PCBs.” Several times during Rick’s presentation, I wanted to slap myself in the forehead and say, “I should have had a V-8!”
June 03, 2019

Board Negotiations: Design Rules and Tolerances

Here are several examples of how a PCB fabricator can deal with various tolerances. Let’s look at “press fit” applications for tool sizes. Typically, a given plated hole or slot is ±0.003” and a typical non-plated hole or slot is ±0.002”. So, what does the fabricator do when a plated hole is called out as ±0.002”? The simple answer is to calculate how much plating there will be in the hole barrel, and then over-drill to accommodate the ±0.002 tolerance.
March 18, 2019

The Bare (Board) Truth: Eliminate Confusion

This column will address eliminating confusion that creates remakes both from the end-user/designer and the fabrication house. Let’s say you’ve asked for a material type on your drawing that is not either readily available or used by your fabricator. Here, you should expect the fabrication house to respond quickly and have all the deviations at once for you to review. This includes any impedance width changes, material types, or copper weights to produce the part. Any deviations regarding drawing notes such as wrap plate requirements that cannot be incorporated due to insufficient space or the extra etch compensation to meet the wrap plate requirement should also be addressed.
November 26, 2018

The Bare (Board) Truth: Getting on the Same Page—A Data Story

Thickness callouts for single-sided or double-sided orders are even more critical. As a fabricator, we can control the thickness of the multilayer by using different combinations of prepregs/cores. If a customer calls out a single-sided or double-sided job as 0.008”, is this the core dielectric or an overall dielectric? If 0.008” represents the core dielectric callout on a 2-ounce finished part, the final thickness would be closer to 0.013”. If the callout for 0.008” pertains to the overall finished thickness, we would need to start at a 0.004” core to finish at approximately 0.009” after plate, surface finish, and mask.
May 02, 2018

The Bare (Board) Truth: Refining Output Data Packages for Fabricators

One of the biggest issues PCB fabricators face is the completeness (or incompleteness) of the data output package we receive from customers on a new PCB. In this column, I am going to present what is needed, from a fabricator’s perspective, for a good output package and why.
November 28, 2016

The Bare (Board) Truth: Hey, They’re Just Vias—or Are They?

I get this phone call once a week: “Mark, what is the smallest mechanical via that can be done by your company?” I reply, “What will the tolerance for the vias in question be?” If they say, “Oh, your standard +/-.003” tolerances,” I must tell them the min via would be around .0078” with a signal pad of at least .014” and an anti-pad of at least .018”. What if they don't have that kind of room?
April 19, 2016

The Top 10 Ways Designers Can Increase Profits

Can you truly increase profitability through PCB design practices? Mark Thompson believes you can. And it starts with a philosophy that embraces DFM techniques. Then you must be ready for the initial release to a fabricator by ensuring that you are communicating all of your specifications and needs clearly to the fabrication house so that you get an accurate quote. Let’s dive in, starting with Number 10 and working our way to the most important way a designer can increase company profits.
June 10, 2015

The Do’s and Don’ts of Signal Routing for Controlled Impedance

In this column, we will once again be focusing on controlled impedance structures, both from the layout side and the simulation side. I will break them down into the sub-categories of the models they represent and the important points to remember when using the various models. I will also be asking questions such as, “Why would a fabricator ask for a larger impedance tolerance?” and “Where does the fabricator draw the line for controlling various structures?”
February 25, 2015

What Will 2015 Bring?

I’ve been thinking over what 2015 might look like, from my point of view at a PCB fabrication company. Let me first start out with some broad overviews of trends from 2014 that I see continuing. On my end, I certainly expect to see more RF work, more hybrid analog-digital PCBs, and more surface finishes for lead-free assemblies. And that’s just the tip of the iceberg.
March 19, 2014

The Bare (Board) Truth: Understanding the Typical CAM Process

Not all board fabricators have the ability to have both CAD and CAM. You may say to yourself, "But a CAM tool should be able to do some, if not all, CAD functions," and that is true; but if you are really getting to the design level, you need to have a design team.
December 24, 2013

The Bare (Board) Truth: Qualifying Your Fabricator - Identifying Winners (and Losers)

Columnist Mark Thompson writes, "Based on today's board complexities, a review should be done prior to quote to make sure no manufacturing issues occur. This is critical when it comes to things like minimum pre-preg interfaces on high-copper coil boards or jobs with unique reference planes for various impedance scenarios."
December 12, 2012

The Bare (Board) Truth: I'm From CAM and I'm Here to Help

In this column, Mark Thompson shows that fabricators are not necessarily meddling in your design; some of them really do want to help make your board right the first time. And he also demonstrates how patience and perseverance can go a long way with a customer!
May 22, 2015

The Bare (Board) Truth: Tips for Getting the Boards You Need

This column is about meeting each customer's needs. Some customers' requirements are as simple as a specific definition for a fiducial size, rail tooling, or orientation feature, while other customers may require special processes. Mark Thompson offers fabricator tips that can help designers get the boards they need.
May 16, 2012

The Bare (Board) Truth: Tales From the Fab Shop

Designers continue to create the same-net spacing violations when relying on autorouters. Surface features connected elsewhere on an internal plane may have copper pour too close to other metal features. Electrically it doesn't matter whether these features bridge, but for most fabricators, any sliver thinner than 0.003" has the potential to flake off and redeposit elsewhere. By Mark Thompson.
March 30, 2012

Design to Fab: Making it Work

A very large customer sent us two 4-layer boards riddled with differential pairs, with no information about any controlled impedances or specific dielectrics. When we asked if these were to be controlled, the customer was most appreciative and realized that some mention of the impedances, threshold and tolerance should have been made initially. When in doubt, talk to the customer!
March 07, 2012

Mark Thompson: IPC APEX EXPO Wrap-Up

It was a mostly sunny week in San Diego, where IPC APEX EXPO returned after a long absence. I thought the San Diego Convention Center was a great choice for a venue. And this year, the engineers and designers on the show floor were looking at new processes and technologies like kids in a candy store.
September 21, 2011

The Bare (Board) Truth: Slow Down and do it Right

You may be tempted to cut corners in an effort to stay on schedule. But cutting corners to save time does not save anything if it results in a new rev. Let's talk about the risks associated with assuming your board house will find and be able to correct errors in your designs. You'll avoid most of these if you slow down and do it right!
August 03, 2011

The Bare (Board) Truth: Four Common Fabrication Questions

A few months ago, I covered the "10 Most Common Fab Misconceptions." In this column, I will take a similar approach and address four of the most common fabrication questions that I hear. These same questions keep popping up, over and over. But I believe I can dispel the myths surrounding these challenges, and explain their solutions.
June 01, 2011

The Bare (Board) Truth: Scene and Heard at IPC APEX EXPO

I'm always amazed at the diversity of people I see while people-watching in Vegas. And this year, we saw a great diversity of new products and processes at APEX. Some were new combinations of older technologies, while others addressed problems in a completely new, different way.
December 01, 2010

The Bare (Board) Truth: Netlist Mismatches Redux

Let's start by clarifying the intent of the netlist compare. I still get requests to just "generate a netlist" based on the customer's Gerbers. As I have said, since the intent of a netlist compare is to compare the design criteria against the exported Gerber files, this would never find a mismatch.
November 03, 2010

RoHS for Fabricators and Designers: Fact and Fiction

Most of you have heard of the European Union's RoHS directive. Some people mistakenly think it's mainly an assembly problem. But how, exactly, does RoHS pertain to PCB fabricators and designers? Is RoHS-compliant the same as RoHS-compatible?
July 20, 2010

Timing is Everything in Controlled Impedance Fabrication

According to Mark Thompson, timing can make or break your controlled impedance board. With many jobs going through turnkey environments, late communication about impedance issues takes valuable time out of the fabrication process and can delay delivery of product, leaving the end-user and the turnkey assembler unhappy.
June 16, 2010

The Bare (Board) Truth: How to Qualify Your Fabricator

This column is written from the viewpoint of you, the customer. What should you look for when qualifying a fabricator? Sure, you want the company to be IPC Class 3 6012 capable and ISO-certified, and you may need them to be ITAR-certified as well. But what other criteria can help you separate the wheat from the chaff, so to speak?
March 02, 2010

Impedance Lines: Keep Them on the Inside

Keeping those impedance-controlled lines on the inside layers of a circuit board is a great idea for a number of reasons. Let's start with the facts: You'll make your fabricator and your customer very happy by remembering to keep them on the inside.
November 24, 2009

More CAM Edits Revealed!

A typical CAM department makes numerous edits prior to fabrication. Today, I will elaborate on inner-layer feature CAM edits, including the addition of flow and starburst patterns and constraints for scored jobs, as well as the process for fabricating edge-plated features.
July 22, 2009

The Bare (Board) Truth: What Happens to Your CAM Files?

What does the CAM department do to your files and what does that mean to you? The following is a brief synopsis of the edits that are likely to be performed at CAM prior to fabrication.
June 10, 2009

The Bare (Board) Truth: Basic Impedance Fab Guidelines, Part 1

When we talk about signal integrity or impedance lines, there are some very basic guidelines to follow. Remember, impedance mismatches cause signal reflections, which reduce voltage and timing margins.
October 16, 2013

A PCB Design Potpourri

In this column, Mark Thompson revisits topics covered in some of his previous columns and fleshes them out with new, updated information. Thompson says, "In this job, I truly learn something every day, and I'm happy to share a few notable nuggets with you."
December 24, 2013

Qualifying Your Fabricator: Identifying Winners (and Losers)

Columnist Mark Thompson writes, "Based on today's board complexities, a review should be done prior to quote to make sure no manufacturing issues occur. This is critical when it comes to things like minimum pre-preg interfaces on high-copper coil boards or jobs with unique reference planes for various impedance scenarios."
March 19, 2014

Understanding the Typical CAM Process

Not all board fabricators have the ability to have both CAD and CAM. You may say to yourself, "But a CAM tool should be able to do some, if not all, CAD functions," and that is true; but if you are really getting to the design level, you need to have a design team.
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