How To Be A Circuit Board Designer - The End

BACK (space) NEXT

There are electronics hobbyists who "do it all"; create their own circuits, complete the board layout, get the design quoted and purchased and fabricated, populate it with components, hand-solder the connections and test the result. But when it comes to circuit board development in the commercial world, no man is an island. You will be interacting with many different people, and you should consider each of them as your CUSTOMERS, each having different needs and expectations.

Here is a brief summary of the people
who will probably need your help:

Your Supervisor or Project Lead

This is so obvious that it probably doesn't need to be mentioned, but the list wouldn't be complete without it. You're being paid to Get The Job Done in the least amount of time for the least amount of money while keeping all your other customers happy (which will make him look good, too!). Don't neglect this customer. So, Let's DO This...

The Electronics Engineer

The engineer (or the person who created the schematic) should be able to provide many details about the performance of the final product. For example, there may be specific nets that have to carry a higher maximum current, or nets that need impedance control. In many cases this information will not be provided to you by default, and you will have to make an effort to seek out as much supporting information as you can, preferably before starting the board layout. It is more difficult to incorporate design parameters into the project mid-stream or after a design review, so the more you can find out about the design in advance, the better off you will be.

If the CAD system supports it, make an effort to build as many of these constraints as possible into the design at the schematic level, so that certain types of design checking can be automated. Even so, you should review any automated constraints that were added by others before starting the design to make sure you will be implementing them in the manner that is intended. Pay careful attention to every detail that is provided, and take steps to make sure each and every one is addressed at some point in the design process.

I have found it helpful to have a short meeting with the engineer before I start, to record as much information as I can about the design. There are hundreds if not thousands of details to manage for every design, so any process you can implement to help manage them will save time and reduce the chance for error. I created a simple form to keep track of these details; and as a convenient place to record notes, drawing numbers, contact info, etc. As part of a final design review, I use this form as a checking tool to make sure nothing falls through the cracks.

Here's a form that you can use to
record information for new designs:

Returning to the topic of customer support, the engineer is expecting you to take the schematic diagram and return a physical board that can be used to build the circuit and test the ideas behind it. In this respect the engineer is your primary customer, and your ability to incorporate the schematic (along with everything else everyone else tells you) into a working design will make or break your reputation. Along with learning what it takes to perform this job successfully, I encourage you to be a good listener when working with your engineer.

The Mechanical Engineer

You will be transforming a 2-Dimensional schematic diagram into a 3-Dimensional product. Except for specific component package sizes called for by symbol attributes, nothing else in the schematic controls the physical size of the design. Unless the design is a simple test board without size constraints or mounting requirements, you will have to get information about the physical dimensions from somewhere else, usually from someone performing the function of a Mechanical Engineer (ME). In addition to defining the maximum area you can use and the shape of the board outline, a mechanical engineer may also be providing locations for mounting features, and for specific components that must be placed precisely (such as mating connectors, switches or indicators). If the design will be mounted inside a housing or enclosure, the mechanical engineer can also help define component keep-out areas and height restrictions.

From this description, it seems that we are the customers of the Mechanical Department. Truly, we are. So why would we list the mechanical engineer as one of our customers? Many of the modern CAD tools used by many companies allow the transfer of design data back and forth between the electronic and mechanical design departments. Several different translating methods and file formats have been developed to facilitate communication between systems. If a process can be worked out in your company to share data between CAD systems, duplication of effort and errors caused by miscommunication can be minimized.

You may be able to generate data describing your circuit board layout that the ME can use in design reviews and to produce final documentation, and in that respect he is your customer.

The Program Manager

Program Management involves a lot of scheduling, and one of the questions I am most reluctant to answer is "How long will it take?"

I always have the impulse to tell them what they want to hear (and it is my genuine desire to meet their goals), but sometimes I already know that the deadline is unreasonable. Each company is a little bit different in how they assign responsibilities, and in how much extra time you are expected to devote to training, team meetings, documentation, record-keeping, phone calls, email, etc. Keep a log of how you spend your time so you can review previous design cycles before committing an estimate for the next. If you typically average six hours per day on actual design work, or are consistently waiting for other people in a design process flow that isn't optimized very well, you should probably take that into account when you are giving your estimate. As you establish your daily routine you will begin to get a better feel for how much time your typical designs will take.

So, some day not too far in the future, you could be surrounded by a roomful of people in a meeting when someone tries to pin you down to a specific due date, and everyone is hoping you will say "I can do it." The best advice I can give here is "Be honest!". Agreeing to an unattainable goal under pressure will be offset by even worse consequences later on if plans fall apart, and in the long run people will trust you more if you show personal integrity. You might just have to "go the extra mile" for the company every now and then to meet a tight schedule goal, but in even in these cases, it might help if you are prepared to make adjustments. For example, offer to revise your estimate if you can postpone a different priority until later, or postpone some of the routine activities temporarily to give yourself more time to devote to the "hot" design. If you can explain the situation without making it seem like you are making excuses, you may find people are more than willing to help you work something out. Regardless, your partners will be better able to make arrangements knowing the real situation, painful though the truth may be.

The Purchaser

This one is all about the money. I'm using "the purchaser" to stand for the financial interests of your company, and you will have an influence on the cost of any product that incorporates electronics. The sooner you can get the Bill of Materials to the purchaser, the more time they will have to organize inventory and start planning buys for long lead-time items. More time often translates to cheaper prices. As program management is scheduling machine time and resources for the build, the purchaser will need to have all materials delivered prior to the build date. This not only applies to the individual electronic components and miscellaneous hardware, but to the bare board as well. A board ordered for a three-day delivery will probably cost more than twice as much as a more standard ten-day turnaround. In other words, if you miss the due date for having the data available for board fabrication, you may either have to postpone the build or pay more money to have the boards ready in time.

Secondly (but just as importantly), accuracy is your highest priority. One mistake will mean putting the order on hold waiting for new data if caught early enough, but could have even greater consequences. Another expensive board order is bad enough, but even worse is having to scrap entire assemblies because they don't function correctly.

If you aren't absolutely sure what you are sending out,
take the time to check it!

There are many other areas to consider related to the final cost of a product, like making an effort to improve yield or material usage, reducing layer count, removing wasteful assembly steps, etc. Several of these topics will be mentioned in other sections.

The Bare Board Fabricator

This customer will be using one of your major data packages, which will contain everything needed to manufacture and test a bare board. The board fabricator needs data for each layer (which may include soldermask and silkscreen), data for drilling holes, and a fabrication drawing or some way to interpret the design parameters; not only for the build but also for quoting and quality inspection purposes (this could be a web-based ordering system instead of an actual drawing). Including a netlist is strongly encouraged if your fabrication partner can use it for comparison. We will cover this in more detail as we go along in this tutorial, so for now I will just state the obvious; make sure the data you send is complete, that each file is labelled properly, and be sure to include a README file or at least your Contact Information (phone and email) for anything that could be confusing.

As you gain more experience you will be able to answer this question for every design, "Can this product be manufactured using only the data supplied? Without any other written or verbal communication?". Some boards are in production for over twenty years, and you don't need anyone to come "looking for you" after you have moved on to other activities. It is better to discuss a build in advance than to risk an entire order of bad boards, so the slightest discrepancy or inconsistency will cause the fabricator to put your job ON HOLD until it can be resolved.

Some designs will have constraints that make fabrication very difficult and time intensive, using specialized materials, processes and equipment. As long as this is understoood by all partners in advance this is perfectly acceptable, but good customer support in this area is not only a matter of sending complete data packages, but also involves selecting design features that will make board fabrication a smoothly running, reliable process. For example, unless you have a good reason for doing so, don't use extremely thin traces when there is room for wider ones, don't drill small diameter holes if larger diameters will work just as well, etc. (more about that later...)

The Assembler

This customer will take your bare board and put all the components on it, and solder everything together. For many products they will also take the finished circuit board assembly and mount it in an enclosure with all of the mechanical hardware needed, brackets, heatsinks, cables, overlays, potting and adhesives if required, etc. (and may even perform packing and shipping to the end user)

What the assembler needs from you is a data package containing some type of assembly drawing showing the board and component labels with related notes. They need placement data for component locations and orientation, they need a component list or Bill Of Material (BOM) and they may also want a netlist and/or schematic for reference. They will also need to know what standard will be used to inspect the workmanship for acceptability.

Final Test

Since no manufacturing process is perfect, mistakes will happen along the way. The goal is to identify errors as soon as possible, and different tests have been developed to catch inferior or unacceptable product before it moves on to the next step. For example, for multi-layer boards, an Automated Optical Inspection system (AOI) may be used to scan each layer of etched circuitry before they are all laminated together. Catching an open or short on a layer BEFORE lamination saves scrapping all the other good materials that would have been laminated to it and then thrown away. Another type of AOI uses a camera to check the orientation of every polarized component after placement, to make sure no parts have been soldered incorrectly before sealing them into housing at final assembly. Catching it early is much easier than troubleshooting a bad assembly later on, saving much time and effort.

Most of these tests use data that you have already provided in the fabrication package, but one in particular needs extra effort from you. For some products that have a high enough volume to make the expense worthwhile, an In-Circuit Test (ICT fixture will be developed to test the final assembled circuit board before it is mounted into the product. For these products you must incorporate test points into the board layout for every net (preferably on the back of the board), and generate an extra file for them containing the test point coordinates. Many CAD systems can help automate this task, and the guidelines for producing good testability will be explained in one of the next sections.

Whenever you start a new design, ask in advance if the volume will warrant the expense of creating a test fixture. You may never have to interact with this customer as long as you provide what is needed (when called for), but you will certainly hear from ICT if your design is not testable.

The Product User

A few paragraphs ago I made the point that the engineer will be your primary customer (and in your typical day-to-day design activities you will find this to be true), but before moving on to the next subject we should take a step back and look at the bigger picture. The needs and desires of the customer who is buying the product should be high on the list of concerns, and as a circuit board designer your decisions can have a significant influence on cost and reliability.

You may be responsible for selecting many of the features in a design, and for making trade-offs between conflicting parameters to achieve a balanced design. Since the bare board is usually one of the most expensive components in a product, and the electronic circuitry has a profound effect on a product's long-term reliability, the choices you make will directly affect the end product and therefore the end-user. You should make an effort to keep this customer in mind when making these decisions.

(Thanks to all the colleagues and friends who taught me)
BACK (space) NEXT