A printed circuit board manufacturer how can continuously produce in the coplanar surface quality, make it meet in today's design closely the distribution of pad deposition is accurate, the amount is continuous and stable solder paste? The proper choice of materials is the most basic. Considering the factors including physical and electrical characteristics, plate stability, impedance characteristic, Z axial elongation, the size and uniformity of surface. In fact, the choice of the material uniformity and surface can affect the surface of the plane.
For the multilayer circuit board is mainly composed of a dense spacing plate, raw material layers should not influence the choice of surface coplanarity. However, the ultra fine pitch products, usually in close circuit characteristics, requirements of plate layer has a smooth surface, usually called "surface enhanced materials". The characteristics of this plate layer is a polyester film containing resin (resin-rich prepregs) - on the traditional 0.0007 "(0.01778mm) of copper foil. Therefore, for the PCB manufacturer, the circuit board smooth surface is to plate layer manufacturer of surface enhanced materials produced by the same way; by a layer of resin rich polyester film adjacent segment as the outer layer of the copper foil. When the line and space in 0.004 "below, the use of ultra-thin copper foil (0.00035) will help to improve the qualified rate.
The ultra fine pitch imaging
Successfully on the ultra fine pitch (0.020 ") Fang Ping (QFP Quad, flat package pack) imaging pad, with today's technology is not a problem. It is connected with signal line spacing element space produces imaging challenge for PCB manufacturers. New technologies, such as direct imaging and laser projection imaging, the future may constitute a fine reproduction. However, UV now most PCB manufacturers are using the traditional (UV) contact printing, glass frame connected by the hinge to improve the alignment of the original, resulting from a printing. This technology can also produce low to 0.003 "in line with interval. But, good control using the following some or all will improve imaging of thin lines qualified rate: exposure unit height calibration light more accurate exposure source developer chemicals, preferred a supply and discharge feed-and-bleed system prior to exposure from dry film up off the cover paper thin (0.001 ") photoresist (photoresist)
etching
And ultra dense spacing imaging, the challenge for the PCB manufacturers is to fine wire and its space, rather than QFP. The etching fine line depends on the equipment condition and to etch the copper foil thickness. Through the use of ultra-thin copper foil, can achieve a higher qualified rate. But before etching the fine line products, the device must be set. This can be accomplished by developing a small test pattern with a 0.002~0.003 "line and spacing, step by step, evenly over a standard size plate. Using this test pattern, the plate is passed from the etching device, and the top surface of the plate is measured, and then compared with the same position of the lower surface. It is necessary to compare the leading edge of the plate to the trailing edge and the width of the wire from the right to the left. If the width of the wire results in a difference of more than 0.0005 of the data, the etching equipment must be fine tuned. Because there are many different etching equipment, so fine tuning is different. Possible improvements across the board and from the top surface and the bottom surface etching uniformity of adjustment includes: the nozzle extension is enhanced to a confluence pipe. This will allow the nozzle to be located closer to the surface of the plate, when it passes through the etching chamber. Change the length of the extension, so that the center nozzle closest to the plate, and then gradually reduce the length to the top of the outer edge of the chamber. Reduce the number of nozzles at the top and bottom of the flow chamber, making the pressure higher. Increasing the valve to the inlet end of the spray pipe in the chamber, allowing the pressure control of the solution.
Additional adjustments may be necessary to achieve the desired uniformity.
The solder layer (Soldermask)
The preferred material for most of the PCB solder is a liquid photosensitive material (LPI, liquid photoimageable). In the design of solder layer dense spacing of QFP, adopt two methods: a Kong Kuai (open block), sometimes called the "gap group (Gang clearance), covered in a row or pad on the vertical level. This design requires no solder layer between the pads, and when the manufacturing error will get the standard wiring diagram in the plate positioning. Another design requires a solder layer between the pads, often called the "net" or "baffle". Use standard equipment, and the net is successful production ranging from 0.003 "width, but requires of solder materials developing very good process control. Any excess bottom erosion will cause the narrow net off circuit board. Therefore, when using the standard on each side of the solder resist layer increased the gap between the 0.002 "(the minimum net thickness of 0.003") method, the gap between the pads must be at least 0.007". However, the use of no net plate can achieve very good results, as long as the gap solder layer pattern and the full block.