Multi-board Projects

Since ancient times, electronic designers have combined different prototype PCB’s in one panel to save costs. If these boards were not particularly complicated you could assemble them by hand, but in this age things are much better done by machine.

Assembly shops have the ability to assemble different boards in the same panel. But when you go to production you are not going to still have boards from different projects in the same panel, but you would if one assembly requires multiple boards and this is the type of project we’re talking about.

If you are designing a product which requires multiple PCB’s, you could design them as one big single PCB and direct the fab to route with tabs or V-score them so they can be broken apart after assembly. I started doing this years ago because it kept the schematic as one rather than needing to break it up in confusing ways.

There are problems with this however. The rest of the design team will receive a 3D model of your one combined board, not the separate boards that can be put where they need to go in the final assembly model. It makes it difficult to figure out if you have correctly placed the connectors when the boards are assembled together.

Altium Designer provides the tools to design a project with multiple separate boards and link them together. We are actually talking two different things and Altium can do both.

One is the panelization which combines the boards. For a long time I didn’t do my own panelizations, I just let the fab do it and that worked fairly well as long as the fab let me approve it. Doing your own panelization can save you some back and forth with the fab but it may cost you a bit because you are not able to guess the optimum panelization for cost. So even in a situation as complex as this it may still be advantageous to let the fab do it. If you want to do your own panelization, you need to create a new PCB in one of the board projects and copy the other PCB or PCB’s into the same project. In the new PCB you place embedded arrays and link each one to one of the PCB’s which will be in the panel. This means not only can you combine multiple PCB’s you can make arrays of each one and the array size of each doesn’t need to be the same.

The other aspect of combining multiple boards is the Multi-board Project. This is a unique type of project in Altium which is a parent project of multiple normal PCB projects. It normally contains two files, the multi-board schematic and the multi-board assembly. The multi-board schematic contains blocks representing each board showing just the connectors. You draw connections between the boards and it makes sure your pinouts match. You push this schematic to the multi-board assembly which shows the 3D models of the different PCB’s. Altium allows you to auto-align them. You can pick a point on one connector of one board and pick the matching point on another board and Altium will automatically align them. You can then check for alignment and collisions so you know the boards will fit together properly and release to manufacturing.

Pick and place machines have been able to combine multiple different boards in the same panel for ages because it’s hardly more complicated than having the same board in an array. If your assembly shop says they can’t do this then you should question whether they can do anything. If they say they need to combine the pick and place files and that means the different boards can’t share any of the same designators, they definitely don’t know what they’re doing. Obviously a single board panel has lots of the same designator all over it so why shouldn’t you have the same designator on completely different boards? Because they are not using the machine’s capability to do different boards and tricking it by combining the pick and place file so it looks like one big board leading back to the problems we started with. If you do this you can’t X-out any of the boards if you need to because the machine thinks it’s just one big board. But really it’s a huge waste of time to try to combine two different pick and place files when the machine software already knows how to do this properly without any hassle.

The advantages of combining project boards in one panel are varied. You will always have the same number of each board. When not combined I’ve seen fabs spit out hundreds of extras of one board which have no mate. The boards come off the assembly line together, since the assembly shop can’t finish just one of the boards, they have to finish the whole panel. I’ve seen final assembly and testing sit idle because they have stacks of just one board without the other(s). Having all your product’s boards in one panel or as few panels as possible is the way to go.

The image attached to this post is just one of many multi-board projects I’ve worked on. It was captured from Altium’s Multi-board Assembly.

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