We will all see or encounter the phenomenon of PCB warping, Shenzhen PCB board warping will cause component positioning prohibition; when the board bends in SMT, THT, component pins are not uniform, which will bring many difficulties to assembly and installation operations, then how to avoid Shenzhen PCB board warping, the following gives us a detailed explanation:
IPC-6012, SMB-SMT's line warpage or twist degree is 0.75%, other boards'warpage degree generally does not exceed 1.5%; Electronic assembly plant's allowed warpage degree (double-sided/multi-layer) is usually 0.70-0.75%, (1.6mm plate thickness) in fact, many boards such as SMB, BGA require warpage degree less than 0.5%; some factories even less than 0.3%;
Calculating method of warpage = warping height / length of warping edge
PCB board warping avoidance:
1. Engineering design:
Interlayer semi-curable sheet placement response; Shenzhen PCB multi-layer core board and semi-cured sheet should use the same supplier products; the outer C/S surface graphics area should be as close as possible, and independent grids can be selected;
2. Drying plate before blanking
Generally 150 degrees 6 - 10 hours, sweep the moisture in the board, further make the resin cured completely, remove the stress in the board; before opening, drying board, no matter the inner or both sides are required!
3. The longitude and latitude direction of the cured sheet should be noticed before laminated laminates are laminated.
Warp and weft shrinkage share is different, Shenzhen PCB semi-cured sheet blanking should pay attention to the warp and weft direction before lamination; core board blanking should also pay attention to the warp and weft direction; generally, the direction of cured sheet coil is warp direction; the long direction of copper clad sheet is warp direction;
4. PCB sample lamination thickness eliminates stress and then cold pressing, trimming edges;
5. Drying plate before drilling: 150 degrees for 4 hours;
6. It is advocated that chemical cleaning should be used for thin plate without mechanical brushing, and fixture should be used for electroplating to avoid folding and bending of the plate.
7. After spraying tin, it is cooled naturally on flat marble or steel plate to room temperature or air float bed cooling, then cleaned; Warping plate treatment: 150 degrees or 3-6 hours hot pressing, using flat lubricated steel plate for heavy pressing