Component placements per hour (CPH) is fundamental to understanding the capabilities of an SMT line. If you want to know how cost competitive, or how many of your PCBAs an operation can build, it all starts with CPH.
In simple terms CPH is the number of components an SMT machine can place in an hour. Because of the mechanical and physical challenges of picking up components of differing sizes and weights, the CPH for particular PCBAs will vary significantly.
Chip capacitors are very small and lightweight. They can be picked up with a rotating head that can carry many parts. The head spins very fast and centrifugal force can cause the parts to fly off. This is the fastest type of component that can be placed, and the heads or machines that do this are often referred to as chip shooters.
Larger BGAs require more suction to pick up, and can fly off if rotated at high speed. So, these parts are usually picked up and placed individually. This is much slower than a chip shooter.
As a result, PCBAs with many parts that can be placed with a chip shooter will have higher CPH potential than products with several large components.
Further influencing base CPH is the physical spacing of components. A placement sequence of the same component placed side by side in a row is much faster than a placement sequence of different components placed all over the board.
How SMT machines are rated for CPH
This is a somewhat controversial topic. Manufacturers of SMT machines may publish a spec that rates their equipment at 175,000 CPH. A number in this range usually means the CPH if the machine only used a chip shooter head and placed a single part in a row. Not a very useful metric.
To address the considerable variance and uncertainty in manufacturer CPH claims, the IPC stepped in with the IPC9850 standard. The standard uses an idealized PCBA that provides a standardized placement requirement used to rate CPH. It is very helpful and much better than the raw specs.
IPC9850 is still a somewhat optimistic placement scenario, so most SMT Engineers will "de-rate" the manufacturers stated IPC9850 by 20-30% to estimate the real world CPH across a range of assemblies.
To recap, a manufacturer might spec a SMT machine as 175,000 CPH capable and an IPC9850 rating of 50,000 CPH, which most SMT Engineers will de-rate to 35,000 CPH (50,000 - 30%).
What's the CPH of a SMT line?
A typical SMT line will have three placement machines, each with their own CPH. How do you determine the CPH of the entire line?
Turns out it's simple, just sum the CPH of all the machines. If a line has three machines placing at 35,000 CPH the line is placing at 105,000 CPH.
Why should you care about CPH?
Understanding CPH is fundamental to understanding and comparing EMS operations. Some examples:
Throughput: If you know the CPH you can calculate expected throughput. The number of placements for your product is the sum of the quantity per column on the BOM. If there are 250 placements, and your product can run at 50,000 CPH, the line can produce 200 boards an hour (50,000 / 200), or 1600 boards per shift. Now if you’re pressed for delivery, you know how many boards to expect your CM to produce (in practice this would be adjusted for efficiency, but's that a different subject).
Evaluation: An SMT operation with higher CPH is usually more advanced. The equipment will be newer, and the supporting processes will be more aligned with high throughput.
Cost: High CPH SMT lines are much more financially efficient. A line operating at real world 100,000 CPH is producing twice the product across the overhead than a line operating at 50,000 CPH. This means it's half the cost, so the 100,000 CPH operation will ultimately have more flexibility on price.
