How to Prevent PCB Warpage
PCB warping is one of the important issues which has a huge effect on board fabrication. Suppose board with installed components is bent after soldering, component feet tend to be disorder, and this PCB board cannot be installed into the chassis or machine socket, therefore PCB board warping will affect the operation of the entire process. To prevent PCB warping, you should pay more attention to the following aspects in the process of PCB fabrication.
Remove Pressure after Lamination
After the completion of hot and cold pressure, cut or milling off the flash on the multilayer board, and then bake 4h in the oven at 150℃, so that the pressure inside the plate can gradually release and completely solid the resin. This step is important and cannot be omitted.
Straighten Board When Plating
Fabricate surface plating and graphics plating on 0.4 ~ 0.6mm ultra-thin multi-layer board should use special folder roller, without this, after plating twenty or thirty microns of copper, the sheet will bend, and difficult to remedy.
Hot Air Leveling the Board
After shocking by about 250℃ on solder bath, hot air leveling PCB board should be put on the flat marble or steel to cool it down, and then sent to the post-processor for cleaning. This is good for avoiding board warpage. To enhance the surface brightness of the lead-tin, some manufacturers put hot air leveling PCB board into the cold water immediately, and do post-processing in one minute. This way will cause board warpage, stratified or blistering on some types of board.
Treatment for Warped boards
Well-managed manufacturers will do 100% flatness check for their printed circuit boards. Pick out unqualified board, put them into the oven, bake them at 150℃ and under pressure to 6 hours, and then cool it down naturally under the pressure. And then check the flatness again, this can save some of the board, however, some boards need the above treatment for two to three times for totally flat.