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6 PCB Design mistakes to avoid designing printed circuit boards

By Terry D Kozlyk, P.Tech.(Eng.) C.I.D.

TECH LAND HAS NOT BEEN the easiest place to work in these past two decades. I feel very fortunate to have practiced my way to better PCB design with several quality-minded companies, or linchpins, as marketing guru Seth Godin would say.

I say fortunate because I have worked for several large multi-nationals with a structured process and process documents. Others have been small technology startups, where you have to make do with many aspects of PCB design such as limited time, limited money and limited resources. Some PCB design environments shared similar practices whereas others developed their own according to what worked well for them. (Read: Strategy for tech startups: Product contract manufacturing and design outsourcing strategy)

As a PCB designer, you have to assemble your team, which should include both your printed circuit (board) fabricator and your chosen EMS provider – (printed circuit board assembly – PCBA) and test. (See: EMS evaluation, and EMS Resources Directory)

Even though EMS providers are external to your company, as a PCB designer, EMS providers are still part of your team so, keep them in the loop because they also want to deliver a quality product.

Below are seven first-hand experiences identified as mistakes responsible PCB designers should not fall victim to.

 

PCB designer mistake 1
Not sending your preliminary controlled impedance board stackup to your intended board fabricator for review (and approval).

Always send your calculated stackup, with all corresponding data for controlled impedance, to your intended printed circuit board fabrication house well in advance of beginning your placement and routing.

 

8-Layer PCB Stackup

 

Quality-minded fabricators typically have their internal processes down-to-a-science that they will not release to you – it’s proprietary. So, they will usually ‘tweak’ your stackup design to account for their proven processes so they can then arrive at your required impedances and manufacturing tolerances.
 

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Likewise, they may also recommend a modified stackup that is less costly, carries lower risk and delivers higher yields.

If you don’t connect with board fabricators early in your design cycle, you could end up finishing your design and sending it to the fabricator – thinking you’ll have a finished board returned in three days – whereas, actually you’ve done nothing more than created a show-stopper.

You could be told your impedances will be out of tolerance, or your design may not even work.

Worst-case scenario, you will have to redo your design from scratch and will have wasted a lot of time. Go tell that to your project manager!

 

PCB designer mistake 2
Not including extra components that may be needed.

I once did a design with a very tight timeline. The circuit designer was still testing in the lab while in parallel, I was in the 11th hour finishing PCB design routing.

The board was very dense with no room for extra surface-mount resistor components.

We were already using 0402 geometries for the discrete semiconductors.

Then it was discovered in the lab that this design did not meet EMI / RFI interference limits. The lab asked, “Can you add these 16 series resistors in series, here, please?” I responded, “Where? There is no room.”

The design ultimately went to fabrication [and assembly] without the resistors installed. So if you are not sure, design extra components in because they are easy to remove in a re-spin and act as a placeholder, just in case they are needed, later.

 

PCB designer mistake 3
Not sending your preliminary component placement to your intended assembly house (EMS provider) – at the initial stages of your PCB design layout.

As with the bare board fabricator, the EMS providers have their own internal processes that we designers don’t always know because, again, these may be proprietary or competitive in nature.

EMS providers need to be able to run design rule check programs or utilities from various third-party software providers or their own custom in-house design rule check to ensure there is sufficient room for placement in high-yield, high volume assembly runs.

Of noteworthy importance, EMS providers certainly know where time is lost with specific components and board-related locations. So, they can recommend where you can give them some additional placement room on the board design, to minimize or totally eliminate rework time, after boards are run thru their SMT line process.

 

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In your search results, you will be able to further target provider options by choosing End Market, then selecting Go.


 
PCB designer mistake 4
Not having design reviews.

You should have several design reviews during critical times of the design flow. Demand that your marketing or sales people are present so they also see if their communique about what type of product they want your team(s) to deliver has been interpreted correctly.

Segments included in this process for critical design reviews, following completion of the schematic, can include review of initial components placement on the correct PCB form-factor board envelope. Then, after the routing is complete, showing the routing layers in hard-copy followed, lastly, by reviewing the completed fabrication and assembly data package — with all of the above completed prior to the package being sent out.

This way all key stakeholders can oversee if their areas of expertise and input will deliver a quality product.

Then, and only then…if everything checks OK, the entire team still has an opportunity to discuss anything that was missed, such as nice-to-have’s, future options demarcation…

Also it is always best to have another set-of-eyes review things that may spot something you may have overlooked.

 

PCB Designer mistake 5
Not doing regular backups of your PCB design work.

I can’t stress this enough. When I was working from a home-office, a heart-stopping moment occurred when I completely blew away three months worth of design work.

While I was moving my mouse on the near-finished layout, my index finger twitched while the mouse cursor was hovering over the filename in my file navigator.

The Result? My entire design was blown away.

I spent the next hour diligently going through all of the scenarios of retrieving such as checking the trash bin, looking into adjacent folders…with no luck.

But, what saved me was that I had become disciplined at finishing my design workday over time by doing a full-backup onto a spare drive.

So I only lost one day’s worth of work and not the three months it could have been. Whew! True story, crazy as it sounds.

 

PCB Designer mistake 6
Not communicating regularly.

Always print off schematics, BOMs, placement layouts and circulate these to your designers as an FYI to them. Keep them in the loop to let them see your progress.

 

Files for a final PCB sign-off: Checklist, fabrication, assembly and schematic drawings

 

It is so easy for miscommunications to occur when the days are long and fatigue, stress and multi-tasking begins to taint one’s perception.

It also shows your circuit designer(s) how much actual time their design is taking so they can give their project manager(s) a heads-up regarding how close (or over) to achieving the promised delivery date the finished design will be.

 

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