Test Your Know How: PCB Separation

In reply to this we would like to publish our results:

   1. Speed => A. Scoring

   2. Cost => C. Lazer Cutting

   3. Stress => A. Scoring 

Scored PCBs are separated using dual "pizza slicer" blades. This action happens very quickly in one swift linear motion. These cuts are generally not selective and cannot reach some areas of the pcb. Complex pcb shapes must have some pre-routing performed on the pcb during fabrication. The final cut following component assembly, happens on the contact areas that remain between adjacent pcbs. These pcb borders must be partially pre-cut into thin v-groove using similar "pizza blades". This makes the final pcb separation very fast and the cut line is a little bit rough on the pcb edges

Lazer cutting is considered an expensive process and is not considered to be fast. Cutting by lazer typically requires many multiple passes over the same cutting line. Each pass removes a thin layer of material in a process known as ablation. There is some risk of conductive carbonised residue on the pcb edges from this. As a result of machine cost, this is generally considered to be the more expensive solution in the current market. It is more typically found in assembly processes that involve thin pcbs such as flex designs. 

Scoring wins ( or loses) again for component stress. In many industries component stress during separation is considered critical. The highest risk components for stress are typically ceramic capacitors which can crack during pcb separation. However, long resistor bodies, such as 1206/1210 or similar, can also crack under such mechanical stress. If mechanically sensitive components are located close to the cutting border ( <5mm or so) then it is advised to pre-route the board in these locations to reduce the stress applied by the scoring blades. 

Note that separation by milling is also considered stressful. However, typically milling tabs are placed in specific locations evenly around the pcb which reduces the total stress impact on the board. 

If you have any other experiences, comments or observations ( or even disagreements) on the points listed above,  then we would be very happy to read and reply to any comments in the section below. Looking forward to hearing any reactions!  

We typically use v-groove and a "pizza" cutter to separate.

This requires components to be spaced away from the edge, we have seen components damaged if too close.

For our high volume designs, (100K +) we use a dedicated fixture to hold the panel and route the boards for singulation. 

This allows components near the board edges.

We have never used mouse-bites or laser cutting.

Thanks for the insight Avant. Interesting to hear your typical use cases! The mouse-bite approach appears to be used for small samples only. The idea is that pcbs can be manually broken apart. Where I came from, this was heavily frowned upon by the Quality Engineers due to stresses. It was not allowed  for series production.  

I would be very interested to hear of anyone who has witnessed lazer separation / singulation . This seems to be reserved for flex designs. Lazer equipment suppliers promote that pcbs can be placed closer together and can possibly enable an extra row of pcbs in the panel, reducing the individual pcb cost.

We use all these methods. They all have their own advantages and disadvantages.

Most often we use Mouse bites and v-scores on the same design.

Laser singulation is great for rigid-flex or very small boards but is a separate and slow machine process that adds cost and time. It doesn't often save board area on an array as it is preferable to route the PCB in conjunction with laser cutting to save time on the laser. There is also a requirement to hold the boards steady during singulation so consideration of the laser cutters requirements is necessary during the PCB design phase.

Hi,

Typically we never use panelized boards. The reason is an extra step is required in post production to de-panel the board. That process can introduce flexing of the board which can cause component fracture in a worst case. In the past years ago as with most designers we had used mouse bites and scoring but modern SMT Placement equipment can literally place components at the edge of the board if needed, not that you would want to do that.

If the board is super small say 1 inch square or slightly larger, Typically a panel will be required. In this case mouse bites work well. On very small boards we usually opt to use a thinner PCB Laminate as opposed to using standard 62 mil FR4. The advantage here is thinner material is easier to route out and de-panel if needed.

I have found that if using an assembly house it is a very good idea to get an idea of the SMD Equipment they have. A good question to ask is do they have a preferred minimum on how close they can place smd components to the edge of the board. In most cases armed with this information it is possible to design a board where the actual finished board is the panel.

Best regards.