Robert Voigt, DDM Novastar
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What is a Stencil Printer?
The first step in a paste, place, reflow assembly operation is the Stencil Printer, which can be manual, semi-automatic, or automatic. This machine dispenses solder paste, using a squeegee, forced over the openings in a stencil onto a printed circuit board.
PRODUCTION VOLUME
The first question to answer is: What production range are you dealing with? This will help you to decide what level of automation you’ll need.
Manual systems
Here, speed is typically not an issue. Fine pitch and accuracy are the most critical factors. Accuracy is determined by how securely aligned the circuitboard is in the machine. There are 4 dimensions to consider for the control method: X, Y, Z and Θ.
Once the board is aligned in the machine, paste is applied using a squeegee. While there are typically a couple of options on all systems, most assemblers will be using a manual squeegee. Some machines have a built-in guide that aids in applying the right amount of solder paste. There are several key points to applying paste properly:
Once the paste is applied, the stencil is lifted off the circuit board, either vertically, or pivoted. There is no practical difference in either of the two lift methods.
Semi-automatic systems
In a moderately high volume environment, several of the functions can be automated to some extent, making the process more efficient, more repeatable, and allowing a higher yield at lower cost.
The following are typically found in semi-automatic stencil printers:
Fully automatic systems
Fig 1: Adjustable camera on vision machine
Here, everything is managed without operator intervention. Systems may include automatic board loading/unloading and auto fiducial alignment for X, Y, Z and Θ positioning. Again, you get what you pay for. If you’re running 2,000 boards/day, more automation may provide significant dividends in terms of quality yield, reduced labor costs, and more control over your process. If you’re spending the kind of money a fully automatic system commands, you will need to perform some serious due diligence on special capabilities that can’t be covered in a short article.
CONSTRUCTION
Regardless of the volume, you’re looking for the best accuracy and repeatability you can get, so once fixturing is set up, you don’t want to waste time recalibrating.
Fig 2: Machine ground holding plate
Accuracy and repeatability are directly related to fine pitch capability, and pitch accuracy is directly related to machine stability. For this reason, construction of the holding plates is critical.
Machines constructed with sheet metal are not nearly as stable as those made using a machine ground holding plate with welded frames. This assures that nothing moves from one board to the next so you can expect repeatable accuracy from board to board.
Another factor affecting print quality is the squeegee type. Squeegee blades are made from several materials, and come in a variety of sizes. Blade types are commonly urethane, metal (most popular), and plastic. Metal squeegee blades typically enable a more controlled print height across the board, and work well with a mix of component sizes.
Some users consider the stencil printer to be the most important purchase of all – consider this quote from the Adafruit forum:
“Spending money on a good stencil printer is a really good idea. You live and die by the quality of the solder paste deposit on your PCB.”
Check out DDM Novastar's wide range of Stencil Printer Machines.
Have questions or need help specifying a machine? Use our contact form for assistance.
VENDOR SUPPORT
Fig 3: View of squeegee
One of the most important aspects of this evaluation (for any SMT machine, frankly) will be support, and the best way to learn how a company treats its customers is by word of mouth. Talk to several customers to find out how happy they are with the machine, the seller, and the support they provide. Where is the manufacturing plant? Can they help troubleshoot software or alignment issues over the ? Do they offer field service? Do they have spare parts in stock for immediate shipment? Remember to ask your supplier about their older machines in the field, and if down the road, spare parts are available, and about their capability to customize a spare part if the machine becomes obsolescent.
Ask what the expected life-cycle of the product is. The industry standard is 7 years. Remember, there is a difference between a true manufacturer and an equipment supplier or distributor.
Double-sided boards or flexible circuits
Do you need a method to print both sides of the board? Check to see that the model you’re considering offers a double-sided nesting fixture, or vacuum fixture to hold down flexible circuits.
Ease of use
Every stencil manufacturer makes different size frames. The stencil printer you buy should be able to accommodate various size mounting frames and/or tubular frames. The manufacturer should also be able to provide adapters for frameless stencils.
Don’t overlook electrical requirements. Be sure the machine you buy will plug-and-play in your environment without new wiring or plan on an adapter/transformer.
Remember: The application of solder paste is the start of your process. It must be right because the rest of the process can’t make up for improper solder placement.
A solder paste printer is a critical step in the SMT production line, which is responsible for printing the solder paste evenly to the designated locations on the circuit board to ensure the accuracy and consistency of the soldering process. How to select the right solder paste printer?
I. Overview
Solder paste printers are based on the printing principle and utilize metal stencils to transfer solder paste onto printed boards. Accurate solder paste printing is the key to quality control in the electronic assembly process as it can directly affect the soldering results.
II. Classification of Solder Paste Printers
Solder paste printing machines can be broadly categorized as follows:
1. Manual stencil printer
Purpose: Suitable for small scale production or laboratory environment.
Characteristics: Operators are required to operate manually, which is less costly but less efficient, and repeatability may be affected by operator’s skills.
2. Semi automatic solder printing machine
Usage: Suitable for small to medium scale production.
Characteristics: Some operations such as board positioning need to be performed manually, but the printing process is automatic with good repeatability and consistency.
3. Fully automatic solder printing machine
Purpose: For large-scale production that requires high efficiency and high precision.
Characteristics: Fully automated operation including board loading, positioning and printing. Generally equipped with an advanced vision system for precise alignment to ensure a high degree of accuracy and repeatability.
4. High-speed solder printing machine
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Usage: Very high volume production, such as the manufacture of cellular phones and consumer electronics.
Characteristics: Designed to be fast and accurate, it can handle a large number of boards in a short period of time.
III. Main Technical Features
1. Vision system
Modern solder paste printers, especially fully automatic and high speed models, are usually equipped with advanced vision systems. These systems are able to automatically detect the position of the boards and ensure accurate alignment between the stencil and the board.
2. Versatility
Certain advanced models are multifunctional and can perform a variety of operations such as solder paste printing and glue dispensing.
Auto-cleaning system: To ensure print quality, some machines are equipped with an auto-cleaning system that automatically cleans the stencil after each print run or during a specified cycle.
IV. Selection Considerations
There are several factors to consider when selecting a solder paste printer.
1. Production scale
large-scale production requires high-speed and efficient machines, while small-scale or laboratory environments may be better suited to manual or semi-automatic models.
2. Budget
Fully automatic and high-speed models usually cost more, but they offer greater efficiency and accuracy. Manual and semi-automatic models cost less, but efficiency and accuracy may be lower.
3. Printing Accuracy Requirements
High-precision applications may require machines with advanced vision systems and auto-alignment features.
V. Future Trends
As the size of electronic components continues to decrease, the accuracy requirements of solder paste printers are gradually increasing. Future presses are expected to be equipped with more advanced vision systems capable of handling smaller component sizes. In addition, the speed and efficiency of the machines are likely to be further improved to meet the demands of mass production.
VI. User-friendliness
In recent years, as technology advances, many solder paste printers have begun to adopt a more user-friendly design. For example, having a touch-screen operator interface makes it easy for operators to change settings, monitor processes and perform troubleshooting. In addition, some advanced models offer multi-language support and graphical user guides, making them easy to use for manufacturers around the world.
VII. Maintenance and Durability
Considering the high cost investment of a solder paste printer, its durability and maintenance requirements are key factors that must be considered by potential buyers. Modern printers are designed to require as little maintenance as possible and are equipped with self-diagnostic features to help users quickly identify and resolve any problems.
VIII. Environmental Considerations
With the growing global focus on sustainability and environmental responsibility, the new generation of solder paste printers are making efforts in this regard. This includes more efficient energy use, reduced waste generation, and the utilization of more environmentally friendly materials and lubricants.
Features of NeoDen ND2 Automatic SMT Solder Paste Printer
1. Advanced up/down visual system, independent controllable and adjusted lighting, high speed mobile camera lens, precisely alignment for the PCB and template and make sure that the printing accuracy is ±0.025mm.
2. High accurate servo motor and PC control which can insure the stability and precision of the printing. Unlimited image pattern recognition technology has the repeated positioning accuracy for ±0.01mm.
3. Suspended printing head which is designed specially in high rigid structure. The computer controls the pressure, speed and movement of the scraper, which can maintain the even and stability of the printing. The structure of scraper beam has been optimized designed. The scraper beam is light and well-formed.
4. The bottom of the board can be cleaned by manual or automatically. The clean function for the bottom of board is automatic and without assists. It can be programmed to control the dry, wet or vacuum cleaning. The cleaning time interval can be free to choose. It can clean all the solder paste inside the boar holes and insure the printing quality.
5. There is composite worktable which can set a thimble and vacuum chamber (optional) according to the size of PCB baseboard. It makes the fixture assembling more fast and easy.
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Post time: Nov-12-