Keyword: PCB factory, printed circuit board, PCB substrate, PCB manufacturing process
In today's rapid development of science and technology, all kinds of high-tech electronic products emerge in endlessly, which makes the demand of printed circuit board increase rapidly, manufacturing difficulty is higher and higher, also more and more strict quality requirements. In order to ensure the high quality and high stability of printed circuit boards, PCB factory total quality management and control of the environment, must fully understand the characteristics of the printed circuit board manufacturing technology. But the printed circuit board manufacturing technology is a comprehensive technology, it involves physics, chemistry, optics, photochemical, polymer, fluid mechanics, the basic knowledge of many aspects, such as chemical kinetics, such as the structure, composition and properties of materials: accuracy, stability and efficiency of process equipment, processing quality; The feasibility of the method; The accuracy and reliability of the testing means and the environment temperature, humidity, cleanliness, and other issues. These problems will directly and indirectly affect the quality of the PCB. Because there are many problems and involved, it is easy to produce a variety of quality defects. Therefore, must be careful to understand the process and produce quality problem, using the process measures to eliminate quickly and improve the production efficiency of PCB. We collect, summarize and organize about this aspect of material, with readers. Here tell me the PCB substrate problems first:
1 PCB manufacturing process change of substrate size
(1) substrate size change for warp/weft direction difference; Due to shear, did not pay attention to the fiber direction, resulting in residual shear stress within the base board, once released, the direct impact on the contraction of substrate size. Solution: determine the change rule of warp/weft direction, according to the shrinkage compensation on the film (light painting before the job). Shear at the same time according to the fiber direction processing, or by the PCB manufacturer in substrate provided character symbol for processing (usually vertical direction of the characters for the longitudinal direction of the substrate).
(2) part of copper foil substrate surface is etched away restrictions to the change of substrate, produce dimensional change when stress relieving. Solution: when designing circuit should try to make the whole board face evenly distributed. If can't also want to must be left in space transition section (position) does not affect the circuit. This because in plank structure of glass cloth, the weft density difference and lead to the differences of the intensity of latitude and longitude plank to.
(3) the brush plate with pressure is too large, tensile stress causes pressure lead to deformation of base plate. Solution: try to brush should be adopted, the process parameters in the best state, and then to brush plate. For thin substrate, cleaning chemical cleaning technology should be adopted or electrolytic process.
(4) resin in the substrate is not completely cured, lead to dimensional change. The solution: take baking method to solve. Especially before drilling for baking, the temperature is 1200 c, 4 hours, to ensure that the resin curing, reduce because of the effect of heat and cold, lead to deformation of the substrate size.
(5) especially multilayer board before laminating, storage conditions, make BoJi plate or half curing hygroscopic, causing poor dimensional stability. The solution: the inner base material treated by oxidation, baking must be conducted to remove moisture. And will handle good substrate in a vacuum drying oven, so as to avoid moisture absorption again.
(6) laminated by the timeliness, caused by excessive flow glue glass cloth deformation caused by. Solution: need to process pressure testing and adjusting process parameters and then clamped down. At the same time can also according to the properties of the half cure piece, selecting proper resin flow.
2 after the substrate or laminated multilayer substrate bending (BOW) and warp (TWIST)
(1) especially BoJi plate placement is caused by the vertical easy cause long-term stress superposition. Solution: the horizontal thin base material should be taken to ensure uniform substrate stress inside any direction, change a base board size is small. Also must pay attention to in the form of the original packaging in a flat shelf, remember to lift weight.
(2) after hot melt or hot air leveling, cooling speed is too fast, or using improper cooling process. Solution: put on the cooling plate of special natural cooling to room temperature.
(3) the substrate in the process of processing, a long time in the hot and cold processing, under the condition of alternating plus substrate stress distribution and cause the substrate bending or warp. Solution: process measures are taken to ensure that the substrate in the cold and hot alternation, adjust the cold and hot conversion speed, to avoid the rapid cold or hot.
(4) base plate curing, cause stress concentration and curving or warping of the substrate itself. The solution: A: press hot-pressing process method for curing processing again. B: in order to reduce the residual stress of substrate, improve the dimensional stability of PCB manufacturing and produce warping deformation, usually adopt preliminary drying process at the temperature 120-1400 - c 2-4 hours (depending on the thickness, size, quantity, etc to choose).
(5) the substrate below the difference of structure of the copper foil thickness different mood. Solution: should according to the principle of laminated, make the differences of two different thickness of copper foil, to take different half curing slice thickness to solve.
3 substrate surface shallow pit or laminated lining with empty and exotic inclusions
(1) copper foil is memory is copper or resin protrusions and foreign particles veiw. The solution: raw material problem, change should be made to the supplier.
(2) after etching found transparent substrate surface, the section is empty. Solution: ditto processing methods to solve it.
(3) especially after etching thin base material has black spot, the state of the particle. Solution: according to the above way to deal with.
The defects of 4 copper substrate surface often appear
(1) copper foil pits or pits, this is because the laminated on the tools used by entities foreign material on the surface. Solution: improving laminated and pressing environment and meet the requirements of cleanliness indexes.
(2) copper foil surface concave points with glue, is due to the clamp used by mould pressing and laminated, with foreign material is directly affected by. Solution: check the mold surface state, improve working environment and repression between laminated can reach the indexes of the technological requirements.
(3) in the process of manufacture, the use of tools is not fit to lead to poor state of copper foil surface. Solution: to improve the operation method, choose the suitable method to process.
(4) the suppression of the surface of the multilayer copper foil in crease, because laminated in sliding and improper flow glue by suppression. Be especially careful when the solution: laminated position accuracy between layer and layer, avoid sliding into the press process. Direct contact with the copper foil surface of stainless steel plate, be especially careful to place and maintain a flat and level.
(5) substrate surface glue point, is likely to be laminated rubber crumb on steel plate surface or copper on the surface. The solution: to prevent rubber crumbs off, half on the edge of a thermal curing can be treated.
(6) have a pinhole depress molten copper foil surface glue to spill may go. Solution: first of all, into the factory of the copper foil the backlight inspection, qualified after must be kept strictly and avoid crease or torn, etc.
White spots or white spot inside 5 plates
(1) the impact of the plate subjected to undue external mechanical forces caused by the separation of local resin and glass fiber. Solution: take measures from the process, as far as possible to reduce or reduce machining excessive vibration phenomenon in order to reduce the effect of external mechanical forces.
(2) local plate by fluoride chemical infiltration, and etching of glass fiber cloth woven points, form a regular white dots (more serious when can see the square). Solution: especially when annealing tin lead alloy coating, easy to take place between goldplating plug and plug pills, must pay attention to choose the suitable annealing tin lead potions and operation process.
(3) Sheet by improper thermal stress can cause white and white. Solution: especially hot air leveling, such as control, infrared hot stamping, failure will cause the effect of thermal stress results in a defect in the substrate.
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