The affect of circuit board warpage to PCB Assembly
Circuit board warpage can cause positioning devices are not allowed; plate bending in the SMT, THT, the parts are not pin sharp, PCB assembly and installation work will bring a lot of difficulties.
IPC-6012, SMB - SMT circuit board warpage or distortion of the maximum degree of 0.75%, other board warpage is generally not more than 1.5%; electronics pcb assembly plant to allow the warping degree (double / multi-layer) is usually 0.70 --- 0.75%, (1.6mm thickness) is actually a lot of boards, such as SMB, BGA warpage board requires less than 0.5%; part of the plant or less than 0.3%;
PC-TM-650 2.4.22B
Warpage Warpage Calculation = height / length of curved edge
PCB warpage prevention:
1. Engineering: prepreg between layers should be arranged;
Multilayer circuit board and prepreg products should use the same supplier;
Outer C / S surface area as close as possible graphics can be used independent of the grid;
2. Baking sheet before cutting
Generally 150 degrees 6 - 10 hours, excluding water vapor plate, and further solidify the resin completely, eliminating the stress plate; expected to open before the baking sheet, either the inner or double-sided are needed!
3. Multilayer laminated plate before the board should pay attention to the direction of longitude and latitude Prepreg:
Not in proportion to the contraction of the same latitude and longitude, cutting laminated prepreg warp and weft directions to distinguish between the former note; Core should also pay attention when cutting warp and weft directions; general direction of plate Prepreg by the volume; CCL long meridional direction;
5. Drilling before the bake plate: 150 degrees 4 hours; 6. Preferably without mechanical grinding thin brush, we recommend the use of chemical cleaning; plating using special fixtures to prevent board bending collapse
4. Laminated thick plate to eliminate after the cold stress, pruning edges;
7. HAL behind a flat plate on a marble or natural cooling to room temperature or cooled air flotation bed cleaning;
Warping board processing:
Hot 150 degrees or 3 - 6 hours, smooth steel plate with 2-3 times the weight of baking;