Connect the Dots: Unraveling the Mysterious BGA Routing Mess

A ball grid array (BGA) device can be a daunting component to route, especially in fine-pitch arrays featuring solder ball counts in the hundreds and pitch values as tight as 0.5 millimeters. With so much new technology requiring high-functioning processors and boards in increasingly miniaturized devices, it’s safe to say higher pin density, reduced lead inductance, and finer-pitch BGA devices will become even more common in our industry.

That means the foreseeable status quo will be less and less space to route traces and vias between pins. BGAs represent a challenge from design through prototyping and manufacturing, but with some sharp attention to detail and a plan focused on best practices, this is by no means an impossible task. Let’s look at how you can take the mystery out of BGA routing and create a PCB design that can handle all those pesky narrow spaces.

Start With a Little Research

BGAs have been around a while, so there are many resources available to provide some guidance and help you not to reinvent the wheel. There are some good online resources that can be very helpful, such as YouTube videos, blog posts, and technical papers. Most of these resources are free to access, leaving you to sift through the marketing noise and extract available learning that will be useful to you. 

Know Where Trouble Can Lurk

Solder joints are where you really need to mind your Ps and Qs. Smaller surface areas reduce the strength of the solder connection and increase the risk of fracture. Thermal issues can create flex between the component and board and put additional stress on the solder joints. Keep this in mind as you conduct research into BGA best practices.

Vet Your Information Sources

Device manufacturers will often have helpful information on their websites, such as routing examples and land patterns. Typically, the part manufacturer’s footprint is optimized for soldering the part to the board but can leave you with an impossible routing solution. It’s important to learn when to follow their guidance and when to improvise in the name of manufacturability and functionality.

In most cases, it’s acceptable to reduce the BGA pad size sufficiently to allow for vias between the BGA pads. Typically, the BGA pad can be reduced to the same diameter as the BGA ball (nominal dimension) shown on the component datasheet.

Planning Is Key

BGAs of any size require a lot of room around them for all the wires and vias you will need to effectively make all the desired connections. Different board patterns will need optimal fan-outs or escape routing tailored to fit them. Examine each pattern carefully, scrutinizing spacing between solder balls, confirming if they are parallel and equidistant or have greater spacing in one direction, and establishing minimum trace width and spacing (Figure 1).

sunstone_fig1_1020.jpg

Figure 1: BGA solder.

Make sure that the critical signal paths and decoupling capacitors are well situated to maintain signal integrity and reduce inductance. Starting with the via escapes and fan-outs, keep some tried and true tricks in mind, such as high aspect ratio vias, micro-vias, or buried vias that will allow you to utilize real estate on all layers. These can be especially critical in the very large and fine pitch devices. Traces required to route between these pads and vias can also be reduced to provide an escape. You may need to use traces and spaces considerably smaller than the rest of the board in this case.

Adding signal layers is another trick to effective routing. Typically, one signal layer is needed for every two rows of pins, but if the BGA pitch is below 0.8 mm, you will need one signal layer per row. Keep in mind that increasing layers can be a relatively simple way to route the traces, but it can also increase the cost of the board and open the door for reliability issues. In many cases, it’s probably worth evaluating if a change to your layout can reduce the layer requirements.

Pro Tip

Make sure that you are working with a PCB manufacturer up front and understand their capabilities, especially as it relates to these aspects for the BGA routing. It is never fun to spend lots of time on a design and find your preferred vendor simply cannot manufacture it. 

Use Your Design Tool

Many of the design tools today have functions to help make you more successful in your design efforts. Explore some of these functions and use them when they make the most sense for your design. Often, you can assign specific rules around your BGA that may differ from the rest of the board, saving you the time and effort of doing it on a trace by trace basis. 

Good luck! Remember these best practices, and you too can make friends with the mysterious BGA.

Bob Tise is an engineer at Sunstone Circuits, and Matt Stevenson is the VP of sales and marketing at Sunstone Circuits. To read past columns or contact Tise and Stevenson, click here.

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2020

Connect the Dots: Unraveling the Mysterious BGA Routing Mess

10-19-2020

A ball-grid-array (BGA) device can be a daunting component to route, especially in fine-pitch arrays featuring solder ball counts in the hundreds and pitch values as tight as 0.5 millimeters. Bob Tise and Matt Stevenson describe how you can take the mystery out of BGA routing and create a PCB design that can handle all those pesky narrow spaces.

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Connect the Dots: How to Know If a CAD Tool Is Right for You

09-21-2020

The tool that defines PCB designers is our CAD software, and many discover quickly that not all CAD tools are created equally. Bob Tise and Matt Stevenson answer the question, "How can designers find the right CAD tools to fit their particular methodology and needs?"

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Connect the Dots: The Nuts and Bolts of Electrical Testing

08-12-2020

In this column, Bob Tise and Matt Stevenson explore the world of electrical testing. They examine a variety of testing methods, what options to look for in a PCB manufacturer, and how to ensure that you're getting the best value out of the electrical test options available to you.

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Connect the Dots: Reassessing the Risk of Offshore PCB Manufacturing

07-15-2020

Offshore board production has long been considered an effective way to reduce the cost of producing electronic devices here at home, but those savings often demand a higher tolerance for delivery issues and come with lowered expectations for quality. Bob Tise and Matt Stevenson explain.

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Connect the Dots: The Power of Forward Thinking

06-06-2020

Innovation comes in many forms and from more places these days. Bob Tise and Matt Stevenson discuss how innovative electronic devices all contain PCBs, and share pro design tips for bringing new products to the market.

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Connect the Dots: Picking a Prototyping Strategy

05-29-2020

No matter how simple or complicated your electronic project, PCB prototyping is part of its journey from concept to reality. This process of turning the design into something physical can teach you a lot about what needs to be tweaked and improved before your PCB is ready for full production. Bob Tise and Matt Stevenson explain how before you can prototype, you have to design.

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Connect the Dots: Increased Focus on Health and Wellness Transforms the PCB Industry

04-04-2020

Our increased focus on health and wellness drives technology advancement for personal devices and those used in the delivery of healthcare. Bob Tise and Matt Stevenson explain how this trend also drives both PCB production innovation and a long-overdue update of the employer/employee relationship.

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Connect the Dots: The Seven-year Etch

03-16-2020

PCB etching seems like a simple task on the surface, but quite a few things can go wrong during this process. Adhering to best practice and continuous improvement is a must to help avoid issues with your finished board. Bob Tise and Matt Stevenson share their design tips for a better etching process.

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Connect the Dots: You Can’t Afford Not to Consider ISO 9001

02-19-2020

“Produce quality or die” may sound harsh, but for manufacturers in the electronics industry, it is true. The ability to consistently produce a quality product profitably is the baseline for business success; if you can’t do it cost-effectively, then you can’t innovate, develop new products, or open new markets. No one knows this story better than Nancy Viter, VP of operations at Sunstone Circuits.

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Connect the Dots: Design Tips For Layout

01-06-2020

As a PCB manufacturer, we receive hundreds of PCB layouts represented in Gerber format every week. As you might expect, they’re not all created equal. Some of the layouts check every box and roll straight into manufacturing, while others need work before they can be sent to the production floor.

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2019

Connect the Dots: A Penny for Your Thoughts on Copper

11-19-2019

You're probably thinking: “Bob can’t possibly write an entire article dedicated to the use of copper in PCBs.” To that, Bob says, “Hold my beer.”

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Connect the Dots: Build Quality Into Your Boards and Processes

11-06-2019

To the procurement clerk, a PCB may seem like it is just a line item on a bill of materials (BOM) or parts list during the production of an electronic device. At Sunstone, we know differently. The PCB is the building block for all of the components and parts in your electrical project.

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Connect the Dots: A Proactive Approach to Controlled Impedance

10-09-2019

You can save time, money, and effort if you are aware of the impedance math when you sit down to design your board. Gain this awareness by using a good impedance calculator, and you can build the right tolerances into your design. Impedance testing becomes a double-check of your work instead of the tool you rely on to tell you if your documentation is correct. Documenting impedance requirements properly is more onerous than most people realize. Though it seems simple, PCB documentation is a details game that often leaves knowledge gaps for your manufacturer.

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Connect the Dots: Managing Global Supply Chain Uncertainty

09-03-2019

We are well into the second year of tariff-centric trade policy, and one thing appears certain—uncertainty is here to stay. Though most of the media focus has been on cars and steel or consumer prices and corporate profits, the enduring challenge for both the electronics and PCB industries has been maintaining reliable global supply chains.

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Connect the Dots: Five Best Practices to Ensure Manufacturability

08-01-2019

When you send your design for manufacturing, your partner does not know what type of device the board will be part of nor the conditions in which it will have to perform. It’s common for harsh environments or exposure to mess up a board’s performance. If you call out materials that will not tolerate the end-product’s operating environment, bad things can happen—such as a smoking board, for example. Be sure your board can tolerate thermal stress or solder joints risk breaking and damaging components.

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Connect the Dots: The Future of PCB Manufacturing Doesn't Belong to Robots, but to the Users

07-09-2019

Is the world ready for the consequences of rapid automation? Will the use of robots displace entire categories of workers? Can artificial intelligence really “think”? How will manufacturing, including PCB manufacturing, be affected by all of these smart robots? These questions actually come from a pamphlet published in 1955: "The Age of Automation: Its Effects on Human Welfare."

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Connect the Dots: Accurate Gerber Files Are Mission-Critical for Smooth PCB Manufacturing

05-30-2019

Gerber files can reveal design issues ahead of the quote process and ensure your manufacturer has everything needed to produce your boards correctly. After consulting with Engineering Support Specialist Eric Haugen, we explored some best practices for making sure that Gerber files are accurate.

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Connect the Dots: Preparing for Tomorrow’s Technology Today

05-16-2019

At a recent Sunstone Circuits planning summit, Matt Stevenson, VP of sales and marketing, and Bob Tise had a wide-ranging discussion about emerging technologies and how they will impact PCB manufacturing. The following is an abridged transcript of this conversation.

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Connect the Dots: MakeHarvard 2019: Bigger and Better!

04-09-2019

Sunstone Circuits was eager to return to MakeHarvard as a sponsor and creator of a competition category this year, also serving as both mentors and competition judges. If you were there, you saw us—we were hard to miss in our bright orange vests. As mentors, we were out and about helping students and answering questions.

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Connect the Dots: Exploding PCBs: Don’t Lose Track of Voltage in Your Design

04-01-2019

Managing split planes? Your CAM tool will not do it for you. We see this almost every day—not exploding PCBs, which pretty rare—but rather problems created by having more than one voltage on a power plane layer. From where we sit, this is one of the more insidious and costly challenges facing PCB designers.

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2018

Connect the Dots: Six Tips to Ensure Parts Fit on Your Board

12-12-2018

One of the most frustrating mismatches with alternative through-hole parts occurs when the land pattern matches, but the pin size is off. If hole sizes are too tight, pins may not fit through the holes, or if they do go into the holes, they may not solder well. Solder will need to flow through the gap between the pin and the hole barrel. If there is not enough space to allow enough solder mass to flow through the hole, the circuit board will absorb heat from the molten solder and cause the solder to solidify partway up the hole. This is called a cold solder joint and can result in a premature failure of your circuit.

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Connect the Dots: New Landing Design to Reduce Thermal Pad Failure

11-16-2018

You’ve finally finished your design. All the traces are correct and the IC landings are to the manufacturer’s specifications. A short run of test boards performs perfectly. For best results, you select a reputable domestic board house for production and a quality assembly shop to do the soldering. When the finished boards arrive, everything looks great. You’re in high spirits and congratulate yourself on a job well done. Then the reports start coming in.

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