How to prevent warping of multilayer circuit boards?
The allowable warpage and distortion of the
surface mount of the multilayer wiring board are 0.75% and 1.5% of the . Compared with IPC-Rb-276(1992 edition), the requirements for surface mount printed circuit boards have increased. At present, whether it is a double-sided circuit board or a multilayer circuit board , the warpage allowed by each electronic assembly plant is usually 0.70-0.75%, and the board warpage requirement for many SMT and BGA is 0.5%. Some electronics factories are pushing to raise the warpage standard to 0.3 percent, and testing warpage is done according to gb4677.5-84 or ipc-tm-650.2.4.22b.
2. multi-layer circuit board requires very flat
In the automatic insertion line, if the printed multi-layer circuit board is not flat, it will cause errors, which will cause the components to be unable to be inserted into the holes and surface pads of the plate, and even damage the automatic insertion machine. Multi-layer circuit boards and components will bend after welding, the component feet are not easy to cut and trim, and they cannot be installed on the chassis and sockets in the machine. Even the assembly factory is bothered by board warping. Nowadays, printed boards have entered the era of surface mounting and chip mounting, and multi-layer circuit board manufacturers will inevitably have stricter and stricter requirements on board warpage.
In the process of 3. production, prevent the plate from warping
1. Straighten the thin plate during electroplating
. When using the thin multi-layer circuit board of 0.6~0.8mm for plate surface electroplating or drawing electroplating, special pinch rollers should be made. After the sheet is clamped on the automatic plating line, the entire clamping roller is connected to the clamping roller with a round bar, and the clamping roller and the entire coil are pulled so that the plated coil is not deformed. If this measure is not taken, the sheet bends after plating a copper layer of 20 or 30 microns and is difficult to remedy.
2. Longitude and Latitude of Semi-cured Board After lamination,
Semi-cured Board has different shrinkage rates in warp and weft directions. Materials and repeated layers must be distinguished in warp and weft directions. Otherwise, will easily cause warpage after lamination, and even the pressure drying board will be difficult to correct. The reason why the warpage of the multilayer wiring board is that the latitude and longitude of the prepreg are not clear, and disorder occurs.
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