Even though we have been manufacturing smt products in high volume for more than two decades, less than 10% of companies have first pass yield fpy of more than 90%. Improving first pass yields and smt line utilization for. Six sigma rolled throughput yield spencer graves 2 spencer graves. This makes smt process capability the key measure to smt quality. First pass yield fpy, also known as throughput yield tpy, is defined as the number of units coming out of a process divided by the number of units going into that process over a specified period of time. The economics of this market trend are unsustainable. Smt board assembly process intel manufacturing enabling guide 6 march 2016. Assembly guidelines for qfn quad flat nolead and son small outline nolead packages. Demonstration of enhanced systemlevel reliability of ultrathin. Pcb surface finishes implication on the smt process. It has been reported that over 50% of smt defects in the final assembly are due to factors involving the stencil printing process. Process of smt manufacturing flow chart of smt process 1.
A free powerpoint ppt presentation displayed as a flash slide show on id. Uncontrolled pcb warpage leads to print and smt defects 4 pcb with thickness. This document is intended to provide guidelines and assis tance in performing and troubleshooting the steps involved in the process of producing printed wiring assemblies incorporating surface mounting attachment of components. Developing a process that includes capability for the assembly of 0201 and 01005 components does not have to be a complicated exercise. Smt surface mount technology, like other smd soldering and pcb assembly technology is not zerodefect soldering process. A stencil should not be treated as a common commodity. It is also more difficult to have high yields for a doublesided smt board, than for a singlesided board. The function of a stencil is to deliver a known and controlled volume of solder paste to device pads on the pcb. For doublesided type i, the board is turned over, and the process sequence just described is repeated.
First pass yield variables line setup incompleteincorrect line setup wrong routing for assembly wrong stencil revision, support plate, paste, adhesive wrong smt program e. Here i will discuss some of the most common faults and causes of smt defects and possible solution and troubleshooting. In addition to the high yield and reliability expected of modern placement equipment, the smt assembly process. Analysis of factors that affect yield in smt assembly. Sometime repairing and replacement of smd components is also done by hand.
For a single sided type i, solder paste is printed onto the board and components are placed the assembly is reflow soldered and cleaned if needed. To compound the problem, the relationships between all the various process variables and yield are unclear. Only good units with no rework or scrap are counted as coming out of an individual process. We discuss the profiling, tools, practical issues, and inspection methods of golden boards, and related tools. The use of thinner components and thinner multiup panel pcbs. Combining business process and failure modelling to increase yield. Welcome to surface mount process the hub for surface mount technology this website has been created primarily to be a technical resource for surface mount process engineers and also for anyone with an interest in surface mount technology smt. There are a myriad of smt defects insufficient solder, bridging, solder balls, voids, etc. A block redundancy scheme is used here, where the entire. Process monitoring strategies for surface mount manufacturing. Smt process recommendations defect minimization methods for a noclean smt process kurt rajewski assistant manager market technology kester 515 e. Key competitive advantages can be obtained through the minimization of process defects and disruptions. There will always be some or the other defect in any electronics pcb assembly in both thruhole and smt. However, the data collected from a standard smt process is typically very noisy due to the natural variability of the smt process itself, as well as the inherent measurement errors of the process monitoring equipment.
Root cause failure analysis of printed circuit board. Because yield accounts for much of the margin, the greatest opportunity to improve profits can be gleaned by eradicating solder defects. The smt stencil is a simple tool typically a sheet of 75200. This standard provides new tools for gauging the yield and reliability of placement equipment yet presents performance results in the traditional metrics. Smt process characterization and financial impact fan li research in motion waterloo on ca abstract portable electronics devices are having more functionality but the size is getting smaller. Pdf packageonpackage pop is one of the major manufacturing strategies for achieving an. An electrical components mounted in this manner is referred to as a surfacemount device smd. Design to reduce smt defects solder paste printing is known as the root cause behind assembly defects. Samtecs searay aeamaeaf series connectors with 500 leads which have a unique solder charge design leads are on a 50 x 50 mil pitch from row to row and two pressfit sfp cages with different lead lengths, 1 with protrusion and 1 with no lead protrusion on an 18. Establishing reliable surface mount assemblies requires robust design and.
Smt board assembly process recommendations this application note describes the board assembly process used in surfacemount technology smt and focuses on the smt componenttoboard reflow soldering process and rework soldering if you are removing or replacing individual components on alreadyassembled boards. Smt surface mount technology manufacturing process. Pdf packageonpackage assembly yield assessment in the. Higher lead free solder solidification and process.
What it means to smt is to place more, smaller and ultra fine pitch devices on pc board. The step cut is formed during the package singulation process, while the dimpled. This article examines some process adjustments made through stencil design and scaling that. Smd or surface mount electronic components ics and chips are soldered to the pcb using surface mount technology. Using specific design rules for substrates and stencils, consistent. Pdf a given surface mount technology set up is analyzed to deduce the. The key to a successful process validation is a thorough understanding of both the manufacturing process and the product specifications. This document addresses the surface mount technology smt board assembly process including reflow soldering smt components to boards, replacing individual components on assembled boards, and samples of rework profiles.
Vendor support and knowledge is typically needed to handle the leds and meet highspeed, high yield smt manufacturing process expectations. As part of its process validation, digicom electronics performed a process map of the surface mount process, including the pickandplace machine. Stencil printing provides a fast, mass solder paste deposition process. Basically it solders smc surface mount components onto the boards through reflow soldering. Smt board assembly process guide download pdf guide. Leds sometimes require specific process parameters for the best pick and place performance. Greeley, co abstract reduction of first pass defects in the smt assembly process minimizes cost, assembly time and improves reliability. Smt, short for surface mount technology, is a method that attaches electronic components onto the surface of pcb.
You are touring a production process and you see numerous steps with inspection followed by scrap or rework. In industry, this approach has largely replaced the throughhole technology construction method of fitting components, in large part because smt allows. Smt process, the placement machine needs to be recon. Redundancy yield model for srams surfacemount technology. Koorithodi, indium corporation in the leadfree era, thermal profiling has a critical role in the smt assembly process.
Ramadan, sttd integration yield, hillsboro, or, intel corp. Approaches to minimize printed circuit board pcb warpage. Thickness process deployed no risk no risk system deployed quality manager stencil initiated with 5% reduction in aperture width in order to reduce paste volume in ic process dept reflow profile. A practical approach to reflow profiling by liyakathali. Improve smt assembly yields using root cause analysis in stencil design greg smith fct assembly, inc. Printing and reflow also exert significant influences on the end result. Spanos, fundamentals of semiconductor manufacturing and process control, chapter 5. Leaded surface mount technology smt the process sequence for type i smt is shown in figure 73. Assembly guidelines for qfn quad flat nolead and son. Strojwas, predictive yield modeling of vlsics, international workshop on statistical metrology, june 2000. Yield and yield management 32 integrated circuitengineering corporation random defects can be traced back to the tools, the people, the processes, the process. Pdf analysis of factors that affect yield in smt assembly.
Their scope in one case was to analysis the relationship between the smt process and the associated yield, in the. While building millions of the same product provides certainly more opportunities to improve yields, a 100% yield is never guaranteea. A way of attaching electronic components to a printed circuit board the solder joint forms the mechanical and electrical connection bonding of the solder joint is to the surface of a conductive land pattern connection does not use through holes or terminals. This paper will present the most common smt yield challenges being confronted today, discuss their root cause, and then. Ppt surface mount technology powerpoint presentation. In other words, 90% of companies are conducting too much rework. Leadfree smt connector process exposure, reliability, quality, and yield assessment for high thermal mass assemblies jimmy chow, john mcmahon, heather mccormick, russell brush, vejeyathaas. The best way to understand the process is through process mapping. Process parameters such as squeegee speed, pressure, and separation speed need to be optimized for the specific solder paste used.
Pick and place machines are used to place components on boards. Critical parameters for stencil performance the stencil plays an important role in the smt printing process, and is a major factor in the overall smt assembly process yield. Mechanical stress and deformation of smt components during temperature cycling and pcb bending application note application note. Improve smt assembly yields using root cause analysis in. Stencil printing yield improvements surfacemount technology. Pcbs with excessive warpage impact paste print quality in print process and solder joint formation during reflow soldering leading to. When problems arise, first do the 5minute overall system check 80% chance that you resolve the problem if specific defects continue to occur, follow logical troubleshooting guidelines. For a doublesided board there are more manufacturing steps and the boards go through the reflow process twice or reflow wave. This is due to the dome material and unbalanced weight distribution of some types of led component.
Stencil printing is a critical step in the electronic assembly process. Assembly soldering process improvement of critical smt. Automationprogrammable processes in surface mount technology research and presentation. Mechanical stress and deformation of smt components. The process uses reflow soldering machine and automated pick and place machines. Pcb surface finishes implication on the smt process yield liya. Surfacemount technology smt is a method in which the electrical components are mounted directly onto the surface of a printed circuit board pcb.
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