PCB Design for Manufacturing: Prevent Via Defects by Talking to Your Manufacturer
One of my ex-girlfriends always used to say, “communication is key for our relationship.” While I may be good at communicating how to reduce EMI on boards, I’m not so good at expressing my emotions. I guess that’s why she’s an ex-girlfriend. Sometimes your feelings toward your manufacturer may resemble your feelings towards any ex-girlfriends. Especially when they tell you that your boards have a <50% yield.
At that point, you may feel like replying with some choice words. Talking is still the answer, just not that kind. Having a discussion with your board manufacturer on the front end will reduce manufacturing defects and fabrication costs.
Those little holes can cause more problems than you think.
Reduce Manufacturing Defects
Everyone wants to date the perfect person, but that’s just not going to happen. Luckily, we can make up for our romantic shortcomings by designing excellent Printed Boards. Like flaws in that perfect person, defects in PCBs tend to show up over time. It’s better to just avoid them altogether by going through your design with your manufacturer. There are lots of things to check through, but your top priorities should be via-in-pads, filled or capped vias, drilling methods, and surface mounted technology (SMT) pads.
Via-In-Pads (VIPs) - You should know what VIPs are, they’re literally vias placed inside pads. VIPs will help you with ball grid array (BGA) breakout but can cause issues as well. If not properly addressed, VIPs can wick thermal solder paste away from components and cause bad connections or tombstoning. You can avoid those problems by plating over any VIPs. Plated VIPs will need to be either filled or plugged, which is where your manufacturer comes in. Talk with them about their methods for filling or plugging, and then plating, any VIPs on your board.
Capped or Filled Vias - In a related note, you should also talk to your manufacturer about any general vias in PCB designs that need to be capped or filled. Some people think they can slightly offset a via from a pad and it will be fine. Those people are wrong. Even if you’re using something like a dog bone breakout, thermal
solder paste can still wick down into vias. So guess what, you have to cap/tent/cover, plug, or fill them. Again, different methods have different pros and cons, many of which will depend on your manufacturer’s capabilities.
Drilling Methods - Let’s keep the via ball rolling. You need to go over how your vias will be drilled with your manufacturer. Through vias are no problem, but drilling can cause some problems when it comes to blind and buried vias. Vias can either be drilled mechanically or with lasers. Lasers don’t usually have many fabrication problems, because they’re awesome. Mechanical drilling, however, is not awesome. Some manufacturers may recommend “peck drilling” your blind or buried vias. Peck drilling is where the drill moves in and out of a blind hole in order to remove drilled material. The problem is, this method can cause material or air to become trapped inside the hole during plating. Air during plating means the via won’t be fully plated, causing connection problems.
Pads - Not only will you need to worry about vias next to pads, you’ll need to think about the pads themselves. If pads are too close together, or if you accidentally forget some solder mask, solder paste will bridge pads. This is usually more a product of forgetfulness rather than bad design. You might miss this mistake, but your manufacturer will be looking for it.
Defects can make you go crazy, like this poor engineer trying to jump a PCB.
Changing your mind after getting married will cost you an arm and a leg. Likewise, you’ll pay a high price for changing designs partway through manufacturing. Checking your designs with your manufacturer can save you a pretty penny.
You should also run your design by your manufacturer to see if it will require expensive fabrication processes. Sometimes your manufacturer can suggest a different design that will be less expensive to fabricate, or a different process that can lower cost. Remember how I was blathering on earlier about how blind vias in PCB designs can be laser drilled or peck drilled. Well, why would you ever peck drill when lasers are cooler and have less risk for defects? Peck drilling is cheap, that’s why. Some manufacturers are actually able to peck drill without causing defects or holes. They could be that mythical perfect partner you’ve been looking for. If your manufacturer can do things like peck hole drilling correctly, they can save you a lot of money. Sweet talk them and see what their capabilities are.
Be sure to check individual as well, for example ct25664aa800.
You may love your partner, but we both know that PCB design is your mistress. Clearly communicating with your manufacturer will help you address the flaws in your relationship with Printed Boards. Enlist their aid in avoiding defects in your vias and pads, and in saving money.
As I said earlier, talking to your manufacturer will help you, but it’s better to design a great board on your own. In order to do that you’ll need some pretty advanced PCB design software. Altium Designer® is the program for you. Altium has already helped designers design for manufacturing. Think I’m just blowing hot air? Hear from Sierra Circuits about how Altium Designer has made their manufacturing job a breeze.
Want to learn more about design for manufacturing? Talk to an expert at Altium.