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The SMT Assembly Process
December 31, 1969 |Estimated reading time: 8 minutes
The Electronic Assembly Suppliers’ Initiative (EASi) Line, featured at ATExpo, in conjunction with the SMTAI, September 26-29, 2005, at the Donald Stevens Convention Center in Rosemont, Ill., and coordinated by Electronics Manufacturing Solutions, Inc., demonstrates a fully functional manufacturing line from start to finish. This year’s line will produce a digital clock packaged in a see-thru case, demonstrating a lead-free assembly process, double-sided surface mount technology and a programmed microcontroller. The EASi Line features sample equipment from material handling and transport, stencil printing, component pick-and-place, selective solder, reflow soldering, X-ray inspection, automated optical inspection, laser marking, robotic point-to-point soldering, rework, depaneling, packaging and microcontroller programming. To assemble the digital clock, the line will use assembly technologies from several SMT companies.
Much like the EASi Line, SMT magazine features its Step-by-Step series, a 10-part look at the SMT manufacturing line. Since its inception in 1994, the Step-by-Step series has given readers a slice of each aspect of the SMT process, breaking the line down and offering educational views from experts in the field.
Step 1: Board Design
Since the inception of computer-aided board design, there has been a strong push to increase design productivity through automation and process optimization. Ultimately, with advancements in circuit design software, there has been a growing demand to support new signal, component or board fabrication technology. Concurrent engineering has been the torchbearer of productivity by applying multiple engineers to the same design. The advantage of parallel design architecture is that it lets multiple designers work on the same design simultaneously without needing to partition the design.
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EASi Line participant(s):
- Data I/O (www.dataio.com)
The following companies are also involved in this step:
- Aegis Industrial Software Corporation (www.aiscorp.com)
- Ansoft (www.ansoft.com)
- BP Microsystems (www.bpmicro.com)
- Mentor Graphics (www.mentor.com)
- Technomatix (www.technomatix.com)
Step 2: Process Control
Lead-free material characteristics have a significant affect on the engineers responsible for implementing and optimizing the lead-free assembly process. It is time for process engineers to understand what is required in the processes that make an SMT manufacturing operation. Process engineers dealing with lead-free need to put more attention into process details. The process window, process tolerances and margin of error are smaller in lead-free processes. There are, however, few new rules for process development and optimization procedures. For the most part, the existing procedures and rules remain. It is the execution of these procedures and rules that will change dramatically.
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EASi Line participant(s):
- ASYS Automation (www.asys-llc.com);
- Cab Technology (www.cabtech.com)
The following companies are also involved in this step:
- Cogiscan (www.cogiscan.com)
- Omron Electronics (www.omron.com)
- Speedline Technologies (www.speedlinetech.com)
- TDK Corp. of America (www.tdk.com)
Step 3: Solder Materials
Proper solder profiling is essential to achieve the best soldering results, which are critical with lead-free soldering. Lead-free processes have brought about a multitude of questions regarding solder material choices, melting temperatures, wetting characteristics and cleaning options. Within the lead-free system comprising solder joints, PCB surface finishes and component coatings, the solder joint material has been considered a challenge. Varying production processes are another challenge. Best practices on the production floor dictate not only production yield but also long-term reliability. Setting the material/process production system correctly is step one. Exercising best practices involves identifying the temperature tolerance level of the assembly system first and, from that, selecting the right approach and proper lead-free alloy for SMT manufacturing.
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EASi Line participant(s):
- Tyco (www.tycoelectronics.com)
The following companies are also involved in this step:
- AIM Solder (www.aimsolder.com)
- Alpha Metals (www.alpha.com)
- Cookson Electronics (www.cookson.com)
- Electronics group of Henkel (www.loctite.com)
- ERSA (www.ersa.com)
- Heraeus Circuit Materials (www.4cmd.com)
- Indium Corporation of America (www.indium.com)
- Kester (www.kester.com)
Step 4: Printing
The solder paste printing process is simple - place the correct amount of solder in the correct location at an acceptable rate. While this goal sounds easy, executing this requires the identification, understanding and optimization of several factors that influence how well the process performs. To develop an optimal PCB printing process, it is essential to consider all aspects of the process. The design of the board being produced, components being placed, materials used and selected equipment must work harmoniously. Suppliers realize they must work together to develop recommended process parameters to satisfy the requirements of customers’ applications.
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EASi Line participant(s):
- Essemtec (www.esssemtec.com);
- MPM (www.speedlinetech.com)
The following companies are also involved in this step:
- EKRA (www.ekra.com)
- DEK (www.dek.com)
- Integrated Ideas and Technology (www.integratedideas.com)
- Juki Automation Systems (www.jas-smt.com)
Step 5: Adhesives/Epoxies and Dispensing
In recent years, three disciplines of fluid formation: manual, semi-automatic and automatic benchtop dispensing systems can be found in a range of applications that have converged in the electronics manufacturing industry. There are few generic manufacturing processes that reach across diverse industries and applications such as benchtop dispensing. Because of equipment and software innovations, benchtop dispensing technology can take its place as a process characterized by accuracy and repeatability.
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EASi Line participant(s):
- Essemtec (www.essemtec.com)
The following companies are also involved in this step:
- Asymtek (www.asymtek.com)
- Dow Corning (www.dow.com)
- Electronics group of Henkel (www.loctite.com)
- Emerson & Cuming (www.emersoncuming.com)
- Master Bond (www.masterbond.com)
- OK International (www.okinternational.com)
Step 6: Component Placement
Leaders in the design and manufacture of metal-dome switch contacts and complementary equipment for membrane switches and related mechanical-switch industries are seeing higher demand. This, in turn, is increasing the need for fully automated high-speed production methods. A reel-to-reel system that handles the first stage of the process, which features placing the metal domes onto a flex-foil substrate, can be developed. Given the required accuracy and placement quality, current pick-and-place equipment can be adapted for reel-to-reel applications. Parallel processing technology with walking-beam transport provides opportunities for customization of reel-to-reel requirements. Simultaneous pick-and-place functions also achieve the high speed required for a competitive solution.
EASi Line participant(s):
- MYDATA (www.mydata.com);
- Production Solutions (www.productionsolutions.com);
- Tyco (www.tycoelectronics.com)
The following companies are also involved in this step:
- Assembléon (www.assembleon.com)
- Creative Automation (www.creativedispensing.com)
- Essemtec (www.essemtec.com)
- Fuji America (www.fujiamerica.com)
- Hover-Davis (www.hoverdavis.com)
- Juki Automation Systems America (www.jas-smt.com)
- MANZ Automation (www.manzautomation.com)
- MIMOT (www.mimot.com)
- Panasonic Factory Automation (www.panasonicfa.com)
- Siemens Logistics & Assembly Systems (www.siemens.com)
- Sony Manufacturing Systems America (www.sonypt.com)
- Speedline Technologies (www.speedlinetech.com)
- TDK Corp. of America (www.tdk.com)
- Ultrasonic Systems (www.ultraspray.com)
- Universal Instruments (www.uic.com)
Step 7: Soldering
There are several important decisions to make when converting to lead-free soldering. Often manufacturers must weight the options and feasibility of purchasing new equipment vs. using existing soldering equipment for lead-free conversion. The implementation of lead-free soldering brings with it several decisions. Whether or not to purchase new equipment, which flux to implement and which solder alloy to use can have a significant impact on the throughput of your operation and, ultimately, your bottom line.
Tin/Lead (top); SnCuNi (bottom)
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EASi Line participant(s):
- Global Automation, Inc. (www.globalautomation.com);
- On-Site Gas Systems (www.onsitegas.us);
- Rehm (www.rehmusa.com);
- Tyco (www.tycoelectronics.com)
The following companies are also involved in this step:
- BTU (www.btu.com)
- CooperTools (www.cooperhandtools.com)
- ERSA (www.ersa.com)
- JNJ Industries (www.jnj-industries.com)
- Manix Manufacturing Inc. (www.manixmfg.com)
- OK International (www.okinternational.com)
- Pace (www.paceworldwide.com)
- Qualitek International (www.qualitek.com)
- Vitronics Soltec (www.vitronics-soltec.com)
Step 8: Cleaning
Printed circuit board (PCB) cleaning - the value-added process of removing surface contaminants that have accumulated during various manufacturing processes and handling - is critical on several fronts. If not properly cleaned, surface contaminants can cause significant defects in the manufacturing process, ranging from poor adhesion of underfill and conformal coatings to lowered surface resistance to dendritic growth and corrosion. Cleaning also has an impact on the final product, from visual appearance to ensuring field reliability and optimum performance.
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EASi Line participant(s):
- Aqueous Technology (www.aqueoustech.com)
The following companies are also involved in this step:
- Kyzen (www.kyzen.com)
- SMarT Sonic (www.smartsonic.com)
- Zestron (www.zestron.com)
Step 9: Test and Inspection
As BGA usage increases on PCB assemblies, more contract manufacturers are implementing X-ray inspection into their test methodology. This inspection method can non-destructively check not only the quality of optically hidden BGA solder joints, but also can be used to confirm overall production process control, such as the level of voiding within solder joints. X-ray inspection of BGAs gives better-resolution analytical images at higher magnifications and oblique angles, allowing far more sensitive and rigorous interrogation of the quality of BGA joints. Once BGAs have been inspected, X-ray inspection can be used to look at other components on the board.
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EASi Line participant(s):
- FEINFOCUS (www.feinfocus.com);
- Scorpion Technologies (www.scorpion-tech.com);
- Viscom (www.viscom.com)
The following companies are also involved in this step:
- Agilent Technologies (www.agilent.com)
- BP Microsystems (www.bpmicro.com)
- Dage Precision Industries (www.dageinc.com)
- ERSA (www.ersa.com)
- Orbotech (www.orbotech.com)
- Phoenix x|ray (www.microfocus-x-ray.com)
- Royce Instruments (www.royceinstruments.com)
- Teradyne Inc. (www.teradyne.com)
- Sieka Machinery (www.seikausa.com)
- VJ Electronix (www.vjelectronix.com)
- VJ Technologies (www.vjt.com)
- YESTech (www.yestechinc.com)
Step 10: Rework & Repair
Given the higher temperature requirements for lead-free soldering and the more delicate nature of array package components, rework stations must now feature excellent profiling and tolerance, as well as offer easy calibration if optimum results are to be achieved and thermal damage avoided. Rework is not going to disappear, as array packages and lead-free processes continue to require post-production processes. While the basic rework steps remain the same, substantial temperature differences between eutectic and lead-free solders mean tighter process control, better temperature profiles and the use of precise rework systems with closed-loop process control are required if high-quality, low-cost rework is to be achieved.
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EASi Line participant(s):
- APE (www.ape.com);
- Beamworks (www.beamworks.com);
- Cab (www.cabtech.com);
- Tyco (www.tycoelectronics.com)
The following companies are also involved in this step:
- BEST, Inc. (www.solder.net)
- Finetech (www.finetechusa.com)
- FocalSpot (www.focalspot.com)
- Pace (www.paceworldwide.com)
- Metcal/OK International (www.metcal.com)
Other companies represented on the EASi Line:
- Conveyors - FlexLink Systems Inc. (www.flexlink.com)
- Benches - Bosch Rexroth (www.boschrexroth.com)
- Flooring - TEK STIL Concepts (www.tekstilconcepts.com)
The ATExpo features exhibits from nearly 600 leading assembly suppliers covering the entire SMT industry. For a complete list of exhibitors, visit www.atexpo.com.