Improve the production capacity of stencil printing machines

When choosing to evaluate automated SMT process equipment such as stencil printing systems, productivity, flexibility, cost effectiveness, and performance are some of the areas that need attention.In addition to freeing people from other tasks, automated equipment has the fundamental advantage of being able to set up each job for a specific product line to ensure optimal operating parameters. These advantages help to achieve all SMT The two highest goals shared in the production process: shortening the production cycle and getting the maximum yield of the product.

Although the current online automatic stencil printing press can shorten the production cycle and maximize the pass rate of the outlet, a new standard called “dual path” has been developed to help improve the SMT assembly process. Productivity.

In most cases, stencil printing will not be the longest time-consuming step in SMT production, and in many cases it will take longer to finish the screen than silk screen. However, evaluate and adopt new methods to reduce the actual printing process time. Significantly, the time saved in actual printing operations can be used to complete other steps, such as solder paste coating, stencil wiping, and post-press inspection. There are several factors that affect the time required for the printing process. It is equally important to shorten the process time.

Video alignment is a key factor in achieving rapid stencil printing.

These factors include: the printing device itself; the speed of PCB transfer and the speed with which the vision system adjusts the PCB; and the speed at which the machine performs the functions of coating, wiping, and post-press inspection. The solder paste itself determines the ultimate speed that can be obtained. It is also a major influencing factor. Even the world's fastest printing press can only print at any printing speed designed with this type of solder paste.

Another major factor affecting the printing speed is the ratio of the component pad size to the size of the template opening. To ensure the fastest printing speed, the component pads on the stencil and printed circuit board must be tightly attached or filled, thus ensuring solder paste. Will not squeeze into the underside of the stencil during the printing process and cause wet bridging. Consider the component's pad using half the component pitch plus 0.002 inches, and the stencil opening is reduced by about 0.001 inches on each side of the pad. For a 0.020 inch For the components of the pitch, the component pad size is 0.012 inches, and the template opening is 0.010 inches, which is a better choice.

Each automation feature has its own advantages.

Coating solder paste

A common problem with canned solder paste operation is that there is too much solder paste placed on the template each time. This is usually done because the silk screen operator saves time for other operations, usually for patching This will cause a large amount of solder paste to dry on the stencil, causing printing defects, or excessive solder paste on the machine, support or camera. Excessive use of solder paste will also allow the operator to quickly use the solder paste Finishing, thus reducing the normal rolling of the solder paste on the template, while increasing the exposure of the solder paste in front of the operator and the air. The solder paste is placed in a container and the solder paste coating system is used to ensure soldering. The paste is applied to the template in a timely and appropriate amount. In addition, the use of a container with a coating system can also reduce the exposure of the solder paste to the operator and keep the equipment and other tools as clean as possible.

Wipe the template

Even a PCB with a flattened component pad and a well-designed printing process requires periodic wiping of the bottom of the stencil. The stencil opening is properly shrunk relative to the component pad and a flat component pad, such as bare copper or Alpha Level will reduce the amount of solder paste that is pushed into the bottom of the stencil, but it still does not eliminate the need for wiping. You can set up an automatic system to perform this operation at appropriate intervals to ensure that the bottom of the stencil is clean and not There will be bridges. Modern stencil printers such as Speedline MPM have automatic wiping systems that can be used for dry rubbing, solvent wiping or vacuum wiping. A dry or solvent-coated wipe can be used. The solder paste on the bottom of the template is wiped off to eliminate the bridge. Vacuum wiping can suck out the solder paste in each opening to ensure that the openings are clean and open, so that the shortage of solder paste is not enough.

You can set the timing to do automatic template wiping to ensure that the bottom of the template is clean and there is no wet bridge.

Post-printing inspection

As the use of array packages increases, such as ball grid array (BGA), chip scale package (CSP), flip chip, and more, the ability to "see" applied solder paste before the PCB leaves the printer It is becoming more and more important. While array packaging offers many advantages, it also brings a disadvantage, that is, the actual solder joint can no longer be seen by conventional inspection methods. Post-print inspection can leave the screen printing machine on the PCB. Make sure the solder paste is applied to each component pad before. The new version of the software released by Speedline MPM has a custom BGA inspection capability that can be set to check the geometry of the 2D post-printing of any actual package.

Post-print inspection ensures that each component pad is printed with solder paste before leaving the screen printer.

In addition to technical problems, long-term factors must be considered, such as the benefits of plant and equipment assets. In this regard, there are many production equipment suppliers in traditional SMT production equipment such as printing presses, placement machines and reflow ovens. On the basis of this, the idea of developing a complete set of production lines was developed, based on a new generation of devices with two parallel conveyor belt designs. This idea is called "dual path".

Dual path thinking

The two-pass idea can be described as follows: In SMT electronics assembly, each path can be independently controlled in a logically ordered sequence to create an effective board flow. This reduces the time lost in the board transport process and extends the SMT equipment to do its own work. Time. A two-pass stencil printer can print on the second board while loading/unloading one board, thus saving overall time.

The dual-channel SMT idea can bring higher yields in a given area.

The two-pass concept also shortens the production line, reducing the need for plant space; in addition, many single-piece equipment has been cut, thereby reducing upfront investment, manpower requirements, facility overhead, and overall operating costs. In perspective, the new assembly system, including the new screen printer, offers greater flexibility with two separate channels. With this type of equipment, a two-pass line can handle several boards simultaneously.

In the electronics and PCB manufacturing process, many assembly work must be done efficiently to achieve maximum throughput and productivity. Careful planning of the assembly process is critical, so that all steps of the SMT process are adjacent to the previous process or under The step process is closely related. It is necessary to consider various types of PCBs with different component densities, different layers, different sizes and different shapes. In order to solve these assembly problems, process engineers must plan the assembly line of the assembly equipment to meet the requirements. The type of PCB being machined. Some lines may be set for maximum flexibility (can be quickly changed), while others may be set to have higher yields, and more settings are for both extremes. Consider together.

However, while setting up the SMT electronics assembly line, it is necessary to consider other aspects beyond production. Although SMT continues to evolve in all aspects of packaging, manufacturing and process, it is “lighter, smaller, faster and cheaper”. The idea is becoming more entrenched. Technologies including high-density internal interconnects will definitely affect the size of the product. The goal of being an electronics assembly manufacturer is to achieve the best manufacturing process. The result is regardless of the involvement. The amount of production or the difficulty of the product, productivity is definitely the most fundamental focus in SMT manufacturing.

Therefore, it is not possible to simply add a press, a placement machine, a reflow system, a washing machine or other SMT assembly equipment, regardless of the plant area involved and the cost of the investor. Instead, it must be recognized The minimum requirements for productivity and profitability, the results of different machines or machine combinations will vary greatly.

For this reason, the manufacturing idea like the two-pass method can bring some obvious real benefits in the silk screen process. The double path can reduce the time required for the loading and unloading plates that do not produce added value, while at the same time bringing more in a given area. Significant manufacturing costs and significant cost savings, in other words, higher yields in a given area.

In PCB assembly like the automotive industry, the production time of each PCB component can be as low as 7 seconds, so the percentage saved by methods like dual-channel is very large. More importantly, the time for these savings is not It can jeopardize the quality of the product. Moreover, by using this method to reduce the need for equipment, the cost advantages in direct labor, maintenance and facilities can also be reflected. In short, manufacturing ideas like dual-channel can be Bring lower procurement costs, lower operating costs, cost-effective production and minimal production space.