On the Order Form
People get ideas. Naturally, they want to act on those ideas. The hold-up comes when they don’t really know what they’re getting into with regards to the PCB. Whether it’s an all-new board or a significant upgrade, the idea-people are really good at under-estimating the effort and technology requirements of their electronic designs. Better visibility of the details will make it easier to manage expectations.
Component vendors do not really help with their reference designs, especially if you are trying to hold down the cost. It behooves them to guide you into a “Cadillac” board since that is what it takes to get the most out of their device. Their design guidelines wind up as wishful thinking when we see our actual cost and size targets. To manage expectations on both sides of this coin, we can use some bureaucracy. Oh, I mean a spreadsheet or a more elaborate survey to get all of the proposed devices to play well together.
The Old Way
It starts like this.
EE “Hey bro, I completed my schematic today, like 90% done. Can you load this netlist? We need the boards kind of soonish”
Me “Load a netlist? Into what?
EE “Doesn’t matter, it’s just a small board
Me “Ok. I have a few cycles after this P-zero thing. When do you need it?
EE “Kind of soonish. Don’t you listen?”
Me “Thanks. I will import the netlist right now to see if we’re good to go.”
EE “Cool. When do we get the boards back?”
We have some back-of-the-napkin estimates we can do based on the total pin count and the net placement area. The ratio of pins per square inch forms a really rough guess that misses potential space hogs. What we want to learn early on is if we have a feasible layout. Refining that down to the optimum size, stack-up and routing geometry requires a longer look at the chaos of a new design.
I like to follow a pre-placement routine of spreading out the constituent components just as the datasheet would have it. Positioning each of these clusters around the outside of the “little outline that could” will show where the most interconnects occur. Try not to get to wound up over the number of “rats” between groups. Instead, focus on the number of critical rats, whatever defines those in your case. The general rule at this point is to minimize the length and crossovers of as many special nets as possible. Play with all of the blocks’ juxtapositions and look for the least inelegant bundle of critical rats. Asking for an elegant solution is probably too much.
Now colorize each group with a unique identifier so you can keep them together before commingling all of the circuits around the brains of the gestating product. Everything wants to be near the center of the action. The most resilient, well-behaved circuits get the worst treatment while the temperamental functions get the VIP locations. We bounce all of this off of our team and find out where we neglected something important and try to make amends.
Let’s Try Something New
What if we put part of this negotiation up front by coaxing some insights out of the inventor. A survey builder can be a low-stress way to ask all of the standard questions that need answers at the start of a design. A mix of yes/no, multiple choice, and written responses as appropriate will surface all of the requirements. A pizza has an order form. Cars, especially nicer ones, have lots of options that affect the price. Why can’t a PCB start with some check-boxes?
You may get some resistance to this form from your internal customers. It doesn’t take long to become the new normal. Chances are, the EE won’t have every answer. The automatic follow up to a missing piece of information is the expected closure date. It’s funny how things that are so obvious to us are not recognized as critical input by the other stakeholders. This is our chance to shed a little light on the requirements. Ask your favorite fabricator if they have some ballpark percentages on the estimated cost adder of the popular options. This data can be a reference or a warning if an expensive option is selected.
Your official form will be tailored to your process variables but could look something like this:
Image Credit: Author - The first page covers the high-level information of who, what and when.
Important information to capture is the list of those who have a say in the design and the schedule expectations. Knowing who will be at the design review is a plus. As long as you have touched base with the stakeholders before we get to the eleventh hour, then the data will have served its purpose.
Image credit: Author - Insert the usual technologies for your product line
The second page is a list of typical cost drivers and options including finish, marking and the all-important solder mask color.
Image credit: Author - Page three captures the assembly data
Putting everything together goes better if you know what level of technology is in use. Environmental conditions and test criteria are established with a few clicks to choose your usual flow or work outside the system. You really need to know when it’s that second thing.
Image credit: Author - the final page is a repository for anything the customer can add
So there it is; about the same complexity as the pizza-app and far shorter than the automobile order form. This information gets us to the starting block so we can work out minimum line widths and air-gaps and so forth using comparable layouts as the historical guide.
By outlining the front-end requirements, the least we’ve done is create awareness that they exist. Better yet if your principals can see the value in providing this information. Getting the correct fabrication notes on to the document is just for starters. The data continues its journey as the e-traveler for the job.
Emphasis should be put on the notion that this is to the best of their knowledge at the time of the writing; subject to change with or without notice. The goal posts are a moving target. We know that. All we’re looking for is a place to start that allows for and reacting to the improvements as they come.
I generated the survey using Google Docs and would love to share it with you. It walks the internal customer through a similar front end that a service bureau or ODM might use to quote a job’s cost and duration. Resistance is expected - AND FUTILE! We will not be denied our token information download when we put so many things in motion to get a board on the ground at the right place and time.