PCB warpage actually refers to the circuit board bending, refers to the original flat circuit board, placed on the desktop at both ends or in the middle of the slightly upward warping, this phenomenon is known to the industry as PCB warpage.
Circuit board warpage formula will be placed on the desktop, the four corners of the circuit board on the ground, measuring the height of the middle arch, which is calculated as follows: warpage = arching height / PCB long side length * 100%.
Board warpage industry standards: According to the U.S. IPC-6012 (1996 version) “rigid printed circuit board identification and performance specifications”, the production of circuit boards allow the maximum warpage and distortion of 0.75% to 1.5% between the process capacity of each factory is not the same for the PCB warpage control requirements there are also some differences, for 1.6 board thickness conventional double-sided For 1.6 board thickness conventional double-sided multi-layer circuit boards, most circuit board manufacturers control PCB warpage between 0.70-0.75%, many SMT, BGA boards, the requirements of the 0.5% range, some of the process capabilities of the circuit board factory can be stronger PCB warpage standard to 0.3%.
In the manufacturing process, how to avoid circuit board warpage?
1. Between the layers of semi-cured arrangement should be symmetrical, proportion of six-layer circuit board, 1-2 and 5-6 layers between the thickness and the number of sheets of semi-cured sheet should be the same;
2. Multi-layer PCB core board with curing sheet should be used with the same supplier’s products;
3. Outer A side and B side of the line graphic area should be as close as possible, when the A side of the large copper surface, the B side of only a few lines, this situation in the etching will be very easy to appear after the occurrence of warpage.
How to prevent circuit board warpage?
1. Engineering design:
Interlayer semi-cured sheet arrangement should correspond to.
Multilayer board core board and semi-cured sheet should use the same supplier products.
Outer C / S surface graphics area as close as possible, you can use an independent grid.
2. Under the material before baking: general 150 degrees 6-10 hours, to exclude water vapor in the board, and further make the resin curing completely, to eliminate the stress of the board; open the material before baking, whether the inner layer or double-sided need!
3. Before laminating the multilayer plate, pay attention to the longitude and latitude direction of the curing plate:
The proportion of warp and weft contraction is different.
Pay attention to distinguish the warp and weft direction before laminating the semi-cured sheet.
The core plate should also pay attention to the warp and weft direction when cutting.
Generally, the direction of the plate curing sheet is meridional.
The long direction of the copper clad plate is meridional.
10 layers 4OZ power thick copper plate.
4. Laminated thick stress relief pressure plate after the cold press, trimming burrs;
5. Bake the board before drilling: 150 degrees for 4 hours.
6. Thin plate is best not after mechanical grinding brush, it is recommended to use chemical cleaning; plating with a special fixture to prevent the board from bending folding
7. Spray tin square on a flat marble or steel plate after natural cooling to room temperature or air-float bed after cooling and cleaning.
Post time: Nov-17-2023