The impact of PCB board warpage on circuit manufacturing is well known to those in the industry. In the automated surface PCB assembly production line, if PCB boards are not flat, will lead to the inaccurate positioning of components, can not be inserted or mounted to the board’s holes and surface mount pads, and may even damage the automatic insertion machine. In addition, if boards occurs bending after loaded with components, component feet is difficult to cut flat and neat, and also can not be loaded into the chassis or machine socket for wave soldering, because some parts of the PCB can not be in contact with the solder surface and can not be welded and other issues.
PCB board warpage causes on the one hand may be the CCL material used (copper-clad laminate) itself warpage, on the other hand, may be due to thermal stress during processing, chemical factors and the impact of improper production processes. Therefore, for the PCB factory, the first task is to prevent the PCB board in the process of warping, followed by the PCB board has been warped for the need to have a suitable and effective way to deal with.
Warped PCBs
PCB warpage prevention methods
1、Preventing the warping of the substrate caused by improper stocking method or increasing the warping of the substrate
Due to the copper-clad laminate in the storage process will increase the warpage of moisture absorption, single-sided copper-clad laminate moisture-absorbing area is larger, if the inventory environment of high humidity, single-sided copper-clad laminate will significantly increase the warpage. Double-sided copper-clad laminates moisture can only seep in from the end face of the product, the moisture absorption area is small, the warpage change is slow. Therefore, for copper-clad laminates without moisture-proof packaging, pay attention to the conditions of the warehouse, try to reduce the humidity of the warehouse and avoid bare storage, in order to avoid the storage of copper-clad laminates to increase the warpage.
Copper-clad laminates without moisture-proof packaging
Copper cladding board placed in an improper way will also increase the warping, such as vertical or copper cladding board on the pressure of heavy objects, poor placement, etc. will increase the copper cladding board warping and deformation.
2, to avoid warping due to improper pcb design or processing technology is not appropriate.
Such as PCB board conductive line graphic unbalanced or PCB board lines on both sides of the obvious asymmetry, one side of the existence of a large area of copper skin, the formation of greater stress, so that the PCB board warping. In the PCB process processing temperature is high or thermal shock, etc. will cause the PCB board warping. For the line graphic there is a large area of copper skin PCB board, it is best to grid the copper foil to reduce the stress.
Asymmetric pattern design on both sides
3, eliminate substrate stress, reduce the processing of PCB board warpage
In the PCB processing process, the substrate many times by the role of heat and to be subjected to a variety of chemical substances. These processes may make the PCB board produce warpage.
4, improve the wave soldering process
Wave soldering or dip soldering, solder temperature is high, the operation time is long, will also increase the substrate warping. Therefore, the wave soldering process needs to be improved, requiring electronic assembly plants to work together.
PCB warpage processing method
1、Flatten the warped board in the PCB manufacturing process
In the PCB manufacturing process, pick out the boards with larger warpage and level them with roller leveler, and then put them into the next process.
2、PCB finished board warping leveling
For the completed PCB boards, the warpage is obviously too poor to be leveled by roll leveler, some PCB factories will put it into small presses for cold press leveling. However, the effect of cold press leveling is not very obvious, and after leveling the board is easy to rebound.
3, warped PCB board bow mold hot press leveling
According to the mechanical properties of polymer materials and many years of practice, it is recommended to use the bow mold hot press leveling method. According to the area of the PCB board to be leveled for a number of simple bow-shaped molds, the use of the following two types of leveling operations: the warped PCB board will be clamped into the bow-shaped molds into the oven to bake the leveling method; the PCB board will be baked soft and then clamped into the bow-shaped molds pressed together with the leveling method.
The leveling efficiency is relatively high, and the proportion of the warped PCB board after leveling is also low. Through these methods, we can effectively solve the problem of PCB warpage and improve the qualification rate of products.
