How to prevent PCB warpage

Warpage of the circuit board will result in inaccurate positioning of the components. When the board is bent at SMT or THT, the pins of the component will not be exactly the same, which will cause difficulties in assembly and installation work.

IPC-6012,SMB--SMT circuit board maximum warp or distortion 0.75%, other board warpage generally does not exceed 1.5%; electronic assembly plant allowable warpage (double/multilayer) is usually 0.70 ---0.75%, (1.6mm thickness) In fact, many boards such as SMB, BGA board requirements warpage less than 0.5%; some factories even less than 0.3%;

PC-TM-650 2.4.22B

Warpage Calculation Method = Warp Height / Curl Length

Circuit board warpage prevention:

1. Engineering design: The arrangement of interlayer prepreg should correspond;

Laminated core boards and prepregs should use the same supplier product;

The outer C/S surface area is as close as possible, and an independent grid can be used;

2, before baking the material

Generally 150 degrees 6-10 hours, excluding water vapor inside the board, further curing the resin completely, eliminating the stress within the board; pre-baking board before the material is opened, whether the inner layer or both sides are needed!

3, multilayer laminate laminating pressure plate should pay attention to the latitude and longitude direction:

The ratio of warp and weft shrinkage is not the same. The prepreg stacking should pay attention to the warp and weft direction before laminating; the core plate should also pay attention to the latitude and longitude direction; the general direction of the plate is the direction of warp; the direction of the longitude of the copper plate is the longitudinal direction;

4, laminated thickness to eliminate stress after the pressure plate, cold trim, trim flash;

5, baking plate before drilling: 150 degrees 4 hours;

6, the best sheet is not mechanically brushed, it is recommended to use chemical cleaning; plating using a special fixture to prevent bending and folding

7. After spraying tin, cool naturally on the flat marble or steel plate to room temperature or air-cooled bed for cooling;

Warp board processing:

150°C or hot-pressed for 3- 6 hours, using smooth and smooth steel plate, 2-3 times baking