How to Design for PCB Assembly Manufacturing
To have your board manufactured there are few considerations that need to be taken into the design. The first thing to consider is, our system runs on rails.
the surface mount placement machines and the wave soldering machine use rails. For the rail system you need at least 5 mm of unpopulated circuit board on two sides for the rail system.
Option B. V-Cut
Option B. Create 5 mm tabs you can snap off.
The option B is to add the 5 mm of material, and add v-cuts so you can remove the 5 mm tabs after the manufacturing process. When adding V-cuts the most important thing to remember is that the machine that cuts the V-cut, needs typically at least 8 cm of length to reliably hold PCB. Sometimes you can push the circuit board house to make them as short as 7.5 cm. Lots of circuit boards are smaller than 8 cm so they must be placed in panels with as many boards as it takes to get up to 8 cm.
In the above picture you can see my Samuraiduino "Arduino clone". The classic Arduino form factor is less than 8 cm. For this reason I placed two of them on the panel. If I separated these two boards with a V-cut I would then need to extend the panel in the vertical direction creating a panel with four boards, so that the vertical V-cut would be at least 8 cm.
As you can see in the picture I separated the two boards with a vertical high-speed router cut. This is a clever way to reduce your panel size. You're welcome to use it in your own design. Just keep in mind the most economical high speed router bit is 2 mm wide. So make your channels are 2 mm wide or more.
In the above picture you can see a PCB for the "Meggy Jr RGB". Because the "Meggy Jr RGB" is longer than 80mm there is no need to panelize it. Here you can see material is added on the top and bottom so that it can fit on the rail system. But there are also V-cuts so that the extra material can be later removed.
Option C. Mouse Bites.
Mouse bites are a common way to hold more exotic shaped PCBs in a panel. When the individual circuit boards are broken out, there is often a small ragged edge. This ragged edge looks a lot like a mouse bite.
Option D. Custom Tray
If you really need your board to have a perfect edges. The way to do this is to have us make custom CNC cut carrying trays to hold your boards. This technique leads to less accurate placement of components. Because the circuit board can potentially move around in the tray.
Option 2. We PANELIZE your boards for you.
In the above picture is an example of computer-generated panelized pcb boards. In this example the PCB fab factory use their software to automatically turn the circuit board design into a panel that is fit for mass production.
What are Fiducials?
In the following photo you can see a fiducial mark. It looks like a mini bull's-eye target. Fiducials are special markings on the circuit board that are designed to be easily recognized by the vision system of the robotic pick and place machine. The pick and place machine can reliably repeat component placements within ±0.01 mm. It's an amazingly accurate machine. This is the kind of accuracy that is needed for the really difficult SMT devices. However the conveyor belt that the board rides on his far less accurate. It's repeatability is probably less than ±2.00 mm. However it doesn't matter how reliable the conveyor belt is because the vision system will find the fiducial marks and recalibrate all of the component placement locations according to the fiducial marks. And that's how the pick and place machine can reliably repeat component placements within ±0.01 mm.
Here you can see where the pick and place grabs the capacitors off the tape and places them on the board.
The pick and place machine not only looks at the circuit board, it also looks at each component before placing it on the board. This way it can make sure that the alignment and rotation of each component is correct before placing it. It also makes sure that it has the correct component and that the component is not noticeably damaged. In the following picture you can see the bottom of one of the Panasonic style surface mount aluminum electrolytic capacitors.
The pick and place machine has its own trash container to place components that it does not recognize. As you can see in the photograph, the vision system uses a black-and-white camera with that gain turned up. If there is a lot of glare on the component, the glare will show up as a prominent shape. In this situation It's easy for the vision system to have trouble identifying the component. It will then place the component in the trash, grab a new component off the real misidentify it and throw that in the trash until the real is empty. Keep in mind it will do all of this at blinding speed. It's these kind of programming problems that make running a pick and place machine expensive. You either need to hire somebody with lots of experience or waste a lot of time and resources watching somebody learn how to use the machine.
How to Design Your Fiducials
The inside dot should be at least 1 mm wide. Everything else needs to be 2 mm in diameter or more. In the following picture you see basically the same fiducial footprint on the circuit board as the frame. The only differences is that the frame does not have copper fill. So you do not see the copper keep out area with a diameter of 2 mm.
As you can see the inside dot is still 1 mm and the outside solder mask ring is 2 mm. All the fiducial designs on this page will work.
How many fiducials do you need?
At a minimum you should have at least three. The vision system needs at least two so that it can no position and rotation and with a third one and can double check the accuracy of its first reading. It's best to place the fiducials as far away from each other as possible. For this reason it's best to place them in the corners. It's also common practice to place extra fiducials next to components with fine pitched leads. This way the pick and place machine can do one more calibration just before placing a more challenging component.
Feel free to place your fiducials underneath large components. It's never a problem to place I fiducial under a through hole component. Through hole components are always soldered after the surface mount process. The next best option is to place fiducials underneath large surface mount components. In this situation the machine operator will program the pick and place machine to place all of the smaller components first then they will place the large component concealing the fiducial never to be seen again.
Anatomy of a circuit board panel
Solder Paste Stencils
For the solder paste stenciling fixture it's extremely common to use the mounting holes that are in the circuit board if there are any. If not then they will use the holes in the frame. That's why there are holes in the frame.
Because the squeegee applies a great deal of downward force is important to support the circuit board in many places to prevent it from buckling under the force.
The squeegee is powered pneumatically, this makes for an extremely reliable process.
Here you can see all the surface mount parts stuck to the board. At this point the solder paste is still little tiny solder balls in a sticky gray paste.
For what it's worth pizzas are some times cooked on conveyor belts also.
This particular pizza oven is from Fischer Equip
Yes we do that. This part is rarely simple. We can typically supply the test frame and a custom-made pogo pin plate to fit your circuit board for about $270