Separating PCB Assemblies Without (Much) Stress

Your contract manufacturer's depaneling methods impact your PCB assembly costs and quality, especially if your company is trying to create smaller products.                 

Printed circuit boards smaller than about six inches are typically fabricated in arrays. After they go through the assembly process the individual boards are separated or “depaneled.”  The methods your manufacturer uses for this seemingly simple step will affect costs and quality.

By understanding the different methods available and talking with the contract manufacturer before finalizing a design, buyers and board designers can avoid expensive problems later.

Depaneling methods can impact a variety of factors, including:

  • Material cost. By fitting as many boards as possible into a standard panel, you can reduce waste and minimize material costs.
  • Labor cost and throughput. Cutters and punches are manual operations, but faster than laser cutting. If you require edge sanding, that adds cost and time.
  • Tooling costs. Punches may require custom tooling to fit the board design. Laser cutting systems are programmable with low setup time. Cutters may or may not require tooling.
  • Tolerances. If your tolerances on board dimensions are tight, or you need to place components very close to the edge of the board, you should look for a manufacturer with laser cutting capabilities.

Board designers can create both the layout and the array drawing to meet the constraints of the process to be used.  It is especially critical to keep surface mount (SMT) components a safe distance from the edge of the board to avoid damage from the depaneling tool.  If engineers don't know what tool will be used, they need to err on the side of safety – perhaps making the board bigger than it needs to be.

Traditional depaneling methods

For rectangular boards, PCB panels are usually fabricated with a v-score between boards.  After components are placed and soldered, we use specialized tools to separate the boards along the score with minimal bending stress. A guillotine type cutter is suitable for thin boards, and a wheel cutter (commonly called a “pizza cutter”) is used for thicker boards.

For boards with curves and other shapes, the bare board panels will usually come pre-routed with tabs or drilled perforations to hold the panel together during assembly. We separate the pre-routed boards at the tabs using a hook tool or a punch.  The tool or punch will leave a rough edge, called “mouse bites,” at the tab locations. If the board has a tight fit or needs to have smooth edges when installed in your product, these may need to be sanded off – an extra step and expense.

Some manufacturers use a mechanical router to depanel curves and other shapes. The router creates less bending stress, but more vibration stress. It also produces a lot of dust, so you should verify that your manufacturer has systems in place to control the dust and keep it off your boards.

All of these methods reduce but do not eliminate bending stresses on the board during depaneling. Ceramic capacitors are particularly susceptible to cracking from bending stress, as are end caps on resistors. Observing the safe distance from the edge of the board helps prevent this damage.

UV laser cutting

UV laser cutting is a newer depaneling method that eliminates bending stresses altogether.  The laser makes extremely narrow, very precise cuts in any shape. It allows components to be placed much closer to the edge of the board, helping you maximize the use of board space in very small PCB assemblies.

PCBs depaneled with a UV laser

PCBs depaneled with a UV laser

In addition, laser cutting lets a manufacturer hold very tight tolerances on the finished assembly size; much tighter than is possible with pre-routed panels. This is a big advantage when the exact board size is critical to the finished product, which we are seeing more often as boards go into smaller and smaller products. Laser cutting may not be suitable for thick boards, due to the time and number of passes that need to be made.

Talking with your manufacturer about depaneling options can help you get the right combination of reliability, material cost, manufacturing cost, precision and throughput.

1 comment on “Separating PCB Assemblies Without (Much) Stress

  1. EdwardThirlwall
    August 13, 2018

    Anything can be done on our own but is it truly safe to do so? If we are out just to cut down on some costs, then we might just be incurring additional unnecessary costs at the end of the day if we are not doing it right. We have to practically have some knowledge in the field to at least be certain that we are handling things right. Should we feel that the whole process is even more troublesome than before, then we probably shouldn't be doing it in the first place. Spending more time isn't really worth it eventually as compared to spending more money if we are unsure of how to do things.

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