PCB Panelization Basics

PCB panelization basics every designer should know

There are a number of factors that impact the cost of your PCB design, but none are more basic than how many parts fit on the manufacturing panel. This guide will introduce you to the common factors involved in PCB panelization and why PCB designers should understand how their PCB fits on the manufacturing panel early in the design process. An optimized panel layout can lead to considerable cost savings. All to often this critical concern is left to the manufacturer. While they are experts at optimizing panel utilization, they can only work with the design they are given. This guide will teach you how to design your PCB for optimal panel utilization from the start.

We'll cover both individual part and array panel layouts as well as ways to analyze the part size for hidden optimizations that can save you money.

The target audience for this guide is beginning PCB designers, but there's also great guidance for experienced designers that are interested in getting the most PCB's per panel to lower PCB manufacturing costs.

Panel layout basics

Let's start with the basics. PCB's are manufactured on panels. The panel can contain an array of PCB's or individual PCB's'. Smaller PCB's such as those for cell phones and similar size devices are typically manufactured in array format. Larger PCB's are manufactured individually on the panel.

The terminology used to describe the manufacturing panel can vary across the industry. Some use terms like grandmother, mother and daughter board to represent panel, array and PCB respectively. Throughout this article we'll use the panel, array and part. Part is the PCB itself.

PCB manufacturing panels almost always have panel borders or a "keep out" area that's reserved for tooling and other manufacturing process needs. PCB's cannot be placed in this area, so the panel borders effectively reduce the available area or "real estate" for the parts and or array's on the panel.

There many panel sizes used in the PCB industry and it's a good idea to learn what your supplier uses. What panel sizes do they use? What's the minimum spacing between the parts on the panel? What's their minimum panel borders?

Panel sizes, part spacing, borders, etc. will be fairly consistent between suppliers because most PCB manufacturers use similar tooling. Some common inch panel sizes are 16 x 18, 18 x 24, 21 x 24 and 21 x 27. The 18 x 24 panel is one of the most common panel sizes in the industry and many manufacturers use a .1" part spacing with .75" panel borders.

The individual part layout - the foundation for all panel layouts

The individual part layout is the simplest panel layout. Even if you’re designing an array, it's important to understand the basics of the individual part layout because the array is effectively the "part" on the panel.

To illustrate the individual part layout, let's use a part size is 5.1 x 8 and the common panel sizes of 16 x 18, 18 x 24 and 21 x 24, with a part spacing of .1 and minimum panel boarders of .75. When we calculate the best layout for each panel size it's not surprising to see that the 21 x 24 (largest) panel gets the most parts per panel. The 21 x 24 offers 9 parts per panel, where the 16 x 18 and 18 x 24 offer fewer parts per panel, but as you'll see shortly, other factors can impact which panel/panel layout is the best.

You’ll notice that some of the parts on the 16 x 18 and 21 x 24 panels are rotated to achieve the best layout. If we look at the other possible layouts for the 16 x 18 and 21 x 24 panels we see that rotating the parts got one more part per panel than the best non-rotated option on either panel. So allowing part rotations provided the best results on two of the three panel sizes. In most cases, you'll get more parts on the panel when you allow rotations.

PCB panels are sheared from larger sheets of laminate and most PCB laminate has a grain direction. The PCB laminate can stretch and shrink in the manufacturing process, usually more so in the direction on the grain, so panels are typically sheared so the grain is in the short dimension of the panel. If you allow rotations on the panel, you’ll have some parts where the grain runs along the length of your part and some where the grain runs along the width. Having some parts manufactured with the gain along the length and others with the gain along the width can introduce some variation between the parts that may affect the part in the assembly process. The grain direction can also impact other aspects of the part such as it's impedance.

Without rotating the parts the 21 x 24 panel is no longer the best choice because it produces the same number of parts per panel as the 18 x 24 panel. The 18 x 24 panel also has a higher part to panel utilization which means less waste and a lower part price. So without rotations, the 18 x 24 panel is the best choice.

The array layout

This guide focuses on array panelization to achieve the most parts per panel and the best PCB manufacturing price. Depending on your design, there may be other design considerations for the assembly process that should be considered.

The PCB array introduces additional factors to consider like the number of parts on the array and how the parts are arranged on the array (the array matrix). Here are a couple of examples of an array layouts. One with three parts on the array arranged in a 1 x 3 array matrix. The other with 12 parts on the array, arrange in a 2 x 6 array matrix. When working with arrays, the spacing between the parts on the array and the array borders must also be factored into the analysis. The array borders are the area that surrounds the parts on the array, much like panel borders. The array borders are waste material that contain the tooling required for the PCB assembly and they are discarded after assembly is complete.

All to often, the array design is chosen arbitrarily without regard to how it will fit on the panel and ultimately the cost of the PCB. Ideally, the array design should be considered as early as possible in the design process, and the chosen array design should be the one that gets the most parts per panel.

Focus on getting the most parts per panel, not arrays per panel

When designing an array it’s important to achieve the highest number of parts per panel, not arrays per panel. You might guess that more parts on the array will equal more parts on the panel, but that's not always true. In some cases, an array with fewer parts will be more efficient and get more parts per panel.

Possible array configurations can vary widely based on the size of the part. Obviously, a larger part will have fewer parts on the array and a smaller part can have more, which means more possible configurations. Let's consider and example with a part size of 1 x 2, a part space on the array of .062 and array borders of .562. The spacing between the arrays on the panel will be .1 and the panel borders will be .75.

Let’s say we'd like a minimum of 4 and a maximum of 10 parts on an array. In this hypothetical case, we've determined that anything less than or more than that it's practical. From the possible array configurations, we need to determine which array design yields the most parts per panel. It is a 4 part array with a 2 x 2 matrix, am eight part array with a 4 x 2 matrix, a 2 x 5, 4 x 1, 1 x 10? There are actually 21 possible array matrix configurations in the range of 4 to 10 parts. To perform a thorough analysis, we'll need to consider how each of the 21 possible array configurations fits on each of the manufacturing panel sizes available to us. It's a complex and time consuming challenge, especially when rotations are allowed. This is why a tool like KwickFit is so valuable. It makes this analysis simple.

When all 21 array configurations are evaluated on the 16 x 18, 18 x 24 and 21 x 24 panel sizes, two optimal array designs emerge for different panel sizes. The 10 part 5 x 2 array gets the most parts per panel on the 16 x 18 and 21 x 24 panels, but the 9 part 3 x 3 array gets the most parts on the 18 x 24 panel. This illustrates the importance of designing the array early and in the context of the manufacturing panel. If a 2 x 4 array was chosen arbitrarily, it would yield less than the optimum parts per panel and cost more to manufacture the PCB.

Also, if the supplier needed to use the 18 x 24 panel size due to process capability limitations, the 10 part 5 x 2 array on the 18 x 24 yields 9 parts per panel less than the 9 part 3 x 3 array. A loss of 9 parts per panel could lead to significant costs over time that could have been avoided with a little up front analysis.

Know how the part size affects the part per panel yield

This is very important and almost always overlooked. Know the threshold at which a reduced part size will increase the parts per panel. Often a small reduction in the part size can lead to improve part per panel yields.

The following analysis was performed by KwickFit and shows that if the part size from our previous example is reduced from 1 x 2 to .934 x 2, the number of parts per panel on the 18 x 24 panel go from 99 parts to 108 parts per panel. This could lead to significant cost savings on a production run.

Reducing the part size by .066 may not be achievable in every case, but having this information at the beginning of the design process is invaluable. If you know the value reducing the part size can have on your costs, you might find ways to trim the part size to achieve the savings.

Panel	Original Qty	Better Qty	Part Size	Change X	Change Y	Cost Savings
16 x 18	60	63	1 x 1.984	0	-0.016	4.76%
18 x 24	99	100	1 x 1.889	0	-0.111	1%
18 x 24	99	108	0.934 x 2	-0.066	0	8.33%
16 x 18	60	63	0.929 x 2	-0.071	0	4.76%
18 x 24	99	100	0.95 x 1.951	-0.05	-0.049	1%
21 x 24	120	126	0.912 x 2	-0.088	0	4.76%
21 x 24	120	130	1 x 1.807	0	-0.193	7.69%
21 x 24	120	126	0.934 x 1.934	-0.066	-0.066	4.76%

Summary

The importance of evaluating PCB panelization at the start of the design process cannot be overstated. Once the design is complete it's often too late to consider changes.

If you're a PCB designer and you create an arbitrary array design leave the panelization details to your PCB to your supplier, there's a good chance you'll pay more for your PCB than you have to. However, if you bake panelization analysis into your design process, you're certain to get the best possible PCB price because you'll go to manufacturing with a design that you know is optimized for the manufacturing panel.