Circuit board warpage will cause inaccurate positioning of components; When the board is bent on SMT and THT, the pins of components are not perfect, which will bring many difficulties to assembly and installation.
Ipc-6012, SMB–SMT circuit board of the maximum warpage or distortion 0.75%, other board warpage is generally not more than 1.5%; Electronic assembly plant allows warpage (double-sided/multi-layer) is usually 0.70-0.75%,(1.6mm plate thickness) in fact, many boards such as SMB,BGA board requires warpage less than 0.5%; In some factories it was less than 0.3%; PC – TM – 650 2.4.22 B. Warpage calculation method = Warpage height/warpage length
Prevention of circuit board warping
Engineering design: the arrangement of semi-solidified sheets between layers; Multi-layer core plate and semi-cured plate shall use the same supplier’s product; The graphic area of the outer C/S plane is as close as possible, and an independent grid can be used.
Drying plate before blanking
Generally 150 degrees 6- 10 hours, eliminate water vapor in the plate, further make the resin cured completely, eliminate the stress in the plate; Drying plate before opening material, both inner layer and double-sided need!
Multilayer laminated plate should pay attention to the warp and weft direction of the plate curing piece:
The warp and weft shrink ratio is not the same, pay attention to distinguish the warp and weft direction before the semi-cured sheet layering; The core plate should also pay attention to the direction of latitude and longitude; General plate curing film roll direction is longitude; The length direction of copper clad plate is longitude direction;
Laminating thick eliminate stress plate after cold pressing, trim burrs;
Before drilling dry plate: 150 degrees 4 hours;
The thin plate is best without mechanical grinding brush, chemical cleaning is recommended; Special fixture is used to prevent plate bending and folding when plating.
After spraying tin in the flat marble or steel plate cooling to room temperature or air floating bed cooling after cleaning;
Warpage processing
150 degrees or hot pressing 3-6 hours, using flat and smooth steel plate pressure, 2-3 times baking!