About DEK paste offset printing technology
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
The rapid development of electronic technology to promote the continuous development of SMT surface mount technology. The electronic components are getting finer and finer; the stitch pitch is getting smaller and smaller; the requirements for component mounting strength and reliability are getting higher and higher. At the same time, the public pays more attention to environmental protection, and the call for a large number of lead-containing production processes is getting higher and higher.
The replacement of traditional lead-containing solder paste with lead-free conductive paste to complete component placement is a new SMT technology produced in this context. Offset is a crucial part of the technology.
Offset printing for surface mount technology (SMT) example 1:
Single-sided PCB interposed mixed wave soldering paste
PCBa surface offset printing, placing components, curing, placing the inserted components on the PCBb surface, wave soldering
Offset for surface mount technology (SMT) Example 2:
Full sided PCB mount reflow process
PCBa surface offset printing, placing components, curing, PCBb surface printing solder paste, placing components on PCBb surface, PCBb surface reflow soldering
Offset printing for surface mount technology (SMT) example 3:
Capsule sealing layer
PCB offset of the completed covering a surface mount cured
Offset printing process
Offset gum material is called according to the requirements will be printed by a screen printing process to a specific planar area, such as on the PCB pads. Thixotropy is a major feature of the offset process in terms of the impact of process parameter perturbations on its process. To offset processing, the wet pad of the PCB suction force, the balance between the interaction and offset printing adhesive portion such that the surface tension of the printed plastic stencil is drawn into the drain hole in the pad. With the next stroke of offset, then screen printed plastic and fill the leak wet suction force is generated in the new pad.
Although the offset printing process and a dispensing process has its similarities, but belong to two different production processes. Compared with the latter, offset printing process has such characteristics:
* Can control the amount of ink very stably. For backing (pad) 5-10 mil pitch to small PCB board, offset printing process can be easily and very stably printed plastic thickness controlled within the range of 2 ± 0.2 mils.
*Offset printing of different sizes and shapes can be realized by one printing stroke on the same PCB board.
Offset printing
The time required for the PCB is only related to parameters such as PCB width and offset speed, regardless of the number of PCB backings (pads). The dispenser dispenses the glue on the PCB in sequence, and the time required to dispense varies with the number of dots. The more glue points, the longer it takes to dispense.
Most customers who use offset technology are often very experienced in solder paste printing technology. Determining the process parameters of the process parameters may be offset printing solder paste printing as the reference point.
Next, we discuss how the printing process parameters affect the offset process.
Stencil
Compared with solder paste printing, the thickness of the metal mesh used for offset printing technology is relatively thicker (0.1-2mm); considering that the glue does not have the automatic paste to the PCB when the solder paste is reflowed. The characteristics of the pad polycondensation, the size of the mesh leakage hole should also be smaller, but it is better not to be smaller than the component pin size. Excessive glue will cause short-circuits between component pins, especially when the placement machine is difficult to achieve 100% full patch accuracy. For PCB boards with small pitch chips, special attention should be paid to chip pin shorts.
Printing gap / scraper
Unlike solder paste printing, the printing gap of the machine is usually set to a small value (rather than zero!) during offset printing to ensure that the peeling between the stencil and the PCB follows the blade printing process. The print gap is usually related to the size of the screen. If zero gap (contact) printing is used, a smaller separation speed (0.1-0.5 mm/s) should be used. Scraper hardness is a relatively sensitive process parameter. It is recommended to use a high-hardness scraper or metal scraper because the low-hardness scraper blade will “hollow” the offset in the stencil leak.
Printing direction
When offsetting epoxy glue, it is recommended to use single-direction printing to eliminate misalignment that may be caused by reciprocating printing. Whisk and scraper blade (flood blade) work alternately, offset blade stroke is completed, the knife whisk whisk glue printing pass back to the starting position.
Printing pressure / printing speed
Rheology glue better than paste. The offset speed can be relatively high, but it can't be as high as it can't make the glue roll on the leading edge of the blade. Generally, the offset pressure is from 0.1 to 1.0 Kg/cm. Offset cloth brush pressure was increased to just scrape the surface of the screen glue.
The voice of experience
* Epoxy glue seem easier than the paste adhered to the blade. If a missing print occurs, check that there is glue on the scraper and the flood blade. Start Offset board, first with the printed plastic stencil leak filled. I.e. multiple printing with a print position of the PCB is placed. Once the stencil leak is filled with the ink, each time the squeegee completes a printing stroke, most of the stencil in the stencil will be printed on the PCB. But also to ensure a very stable amount of printed plastic. For offset printing, keeping the stencil leaks "sticked" by the printing ink itself is the content of the offset printing process, and it is not necessary to make a fuss about it.
* Generally, there is no need to clean the stencil during the offset printing process. If “smear” appears on the back of the stencil, only the “smudged” area should be partially cleaned. And you must use the cleaning agent recommended by the supplier of the adhesive.
*Offset thickness depends to a large extent on the inherent properties of the print. In the case of other parameters constant, the use of different features printed plastic get a different thickness blanket.
* Using offset technology should also be noted to ensure (metal-containing silver) pin compatible glue, BCP plate and the metal element in a production process temperature and humidity conditions.
In the solder paste printing process, a reflow process within a certain range will "automatically" correct iE "patch dislocation." But in offset printing technology, the offset printing process determines that engineers should not "predict" this "automatic correction" function. In other words, offset printing process more challenging for engineers.