What Causes PCB Warpage & How To Avoid It - Miracle Electronics

Imagine, you receive a PCB package, but when you place it onto your application device, you realize that it doesn’t fit into the flat space available! Can you envisage how annoying and bothersome that may be! The reason behind such a scenario is board warping, the unintended change in the geometry of a PCB. A warped PCB is thus an altered PCB, regardless of the shape it forms into, such as bow, twist, etc. In short, a warped PCB is one that does not sit accurately on a flat surface.

What causes PCB warpage?

There are several reasons that could cause PCB warpage, but there are two specific causes – one of them could be layout-related, while the other could be process-related. If the PCB is warped before the beginning of the assembly process, the problem lies between the layout and fabrication. But, if the PCB was flat earlier, and warped after assembly, then the problem lies between the fabrication and assembly.

Design issues causing the warpage – There could be certain design issues that may contribute to PCB warpage, which need to be first and foremost eliminated, before moving onto the fabrication or assembly process. And, in order to eliminate them, you first need to know the main design contributors; some of them being odd shapes, large cut-outs, a thin board, grouping together of heavy components, and uneven copper pour.

Assembly issues causing the warpage – If polyimide or FR-4 is used to build a PCB, and a stack of such bare boards are stored for some time before assembling, they may absorb moisture from the environment, to eliminate which it is customary to bake them for at least 3 hours at 80-150°C first, and then cool them to room temperature before assembling.

Another reason for warpage in large boards may be related to the orientation as the boards enter the reflow oven. In order to prevent uneven heating between the edge of the PCB and the middle, the larger dimension must be placed parallel to the conveyor of the oven.

Small PCBs are generally grouped together to form panels for more efficient assembling, after which they are separated manually into individual PCBs. The separation takes place by either breaking them away or through V-scoring. In the process of breaking away, most of the material between the smaller PCBs is cut away, leaving them joined by only small lands; and if the panelization is large, the cut-outs could lead to warping. On the other hand, V-scoring is where a V-shaped groove forms the separation line, instead of removing a part of the PCB, which prevents warping of the panel during assembly, while making it easier to separate the boards.

How to prevent PCB warpage?

• Storing the PCBs properly before the assembly process is crucial in preventing warpage. Standing them on their edge cannot guarantee that they will be vertical all the while. Moreover, the combined weight of the PCBs will ultimately cause a camber. It is thus important that the PCBs are stored properly, and horizontally on a flat surface.
• PCBs should be stored in an area where the temperature and humidity is under control, because it is usual for PCBs to absorb moisture from the surroundings. And, where it is impractical to control the environment, desiccants can be used to control the moisture.
• Just like PCB fabricators use heat to form multi-layered boards , re-application of heat to warped bare boards can help straighten them as well. But, this may require heavy-pressing the boards between heated smooth steel plates for 3-6 hours and baking the PCBs 2-3 times.

In order to prevent such warpage in your PCBs, you need to ensure that you get your PCB assembly from India from an experienced manufacture, who knows how to take care of every process involved in storing and manufacturing the PCBs well, such that every PCB is built successfully and effectively.