When a printed circuit board experiences warpage, it no longer retains a flat profile, typically curling at the ends.This can lead to significant problems down the line:

· Pick-and-place machines are designed for flat surfaces.When a board has warped, these machines may inaccurately place components onto the face of a PCB.
· Wave solder machines can flood the board with solder when it curves inward, acting like a basin and pooling the solder.
· Warped PCB boards may not fit inside of the end product.Even if the board is still theoretically functional after warping, it cannot be manufactured at scale in this state.

WHAT CAUSES PCB WARPING?

Printed circuit boards can become unusable after warping too much.

PCB warpage occurs due to the presence of imbalanced copper percentages in different layers of the board.   Laminate is made out of several different types of materials: resin, glass fibers, and copper.   Although these layers are flat, they also have “locked-in” stress – when heated to extremely high temperatures, thermal expansion causes movement in the direction of that stress.   PCB board layers thus need to account for this movement in a balancing act.

In multilayer printed circuit boards, it is thus essential that the layers of copper are properly balanced around the central layer, and distributing equal amounts of weight around the center helps minimize the warpage.

The amount of warp and weft associated with different prepregs can be calculated in advance to prevent major warpage.   The closer a prepreg’s warp fill is to another, the less chance for warpage, whereas prepregs with significantly different warp fills in the x and y directions create the potential for warpage.

As soon as a board begins warping, it will continue to warp further throughout the soldering process thanks to the introduction of heat activating the locked-in stress of the board.

PCBmanufacturerChina talk other causes of warping include:

Heat Sinks and PCB Warping

Warping primarily occurs during preheating, and can also occur during the soldering process which applies localized heat to specific areas of the board.   But warping isn’t only specific to these stages.   When a PCB has heavy heat sinks, it can result in localized expansion on the printed circuit board and can sag during the transition phase.

Operating Temperatures

When printed circuit boards are fabricated, they will undergo several periods of intense heating and cooling.   Fabricators must be careful to minimize this processing time as much as possible, while evenly heating both sides of a board.   A good fabricator will communicate with the manufacturer to ensure they understand warp and weft directions before lamination.

FIXING PCB WARPAGE

Once a printed circuit board has become warped, it is nearly impossible to fix. Thus, the best method for fixing PCB warping is by mitigating risks that cause it from the start through smart board design, as well as an understanding of the importance of thermal management in PCB manufacturing.

PCBsupplier China talk In this section, we address several of the methods printed circuit board fabricators and manufacturers employ to avoid or fix PCB warpage.