In-line inspection equipment has become common place in the PCB assembly industry. This equipment is intended to both eliminate defects at an early stage of production and to be used as a process control tool to prevent these defects from occurring in the first place. In practice the full benefits of the applied Statistical Process Control (SPC) methods have typically not been realized even though many of today’s Automated Optical Inspection (AOI) systems come equipped with built-in SPC tools. In this paper we will discuss how a contract manufacturer and an AOI vendor have worked together to develop SPC tools and methods for solder paste printing using a 3D solder paste inspection system.

The use of Chip Scale Packaging (CSP) is rapidly expanding,particularly in portable electronic products. Many CSP designs will meet the thermal cycle or thermal shock requirements for these applications. However,mechanical shock and bending requirements often necessitate the use of underfills to increase the mechanical strength of the CSP-to-board connection. This paper examines the assembly process with capillary and fluxing underfills. Issues of solder paste versus flux only,solder flux residue cleaning and reworkability are investigated with the capillary flow underfills. Fluxing underfills eliminate the issues of flux-underfill compatibility,but require placement into a predispensed underfill. Voiding during placement is discussed. To evaluate the relative performance of the underfills,a drop test was performed and the results are presented. All of the underfills significantly improved the reliability in the drop test compared to non-underfilled parts. Processes such as cleaning or rework that improved the adhesion of the underfill to the PWB solder mask further improved drop test reliability

Automated X-ray inspection (AXI) is more often a part of an effective test strategy for today's PCBAs1 because of the benefits it provides manufacturers in meeting challenges resulting from2:
•?Continued product miniaturization amid increased product functionality
•?Increased time to market and time to volume pressures
•?Growth in outsourcing and contract manufacturing
The structural defect coverage provided by AXI is complementary to electrical test; AXI helps to increase overall fault coverage when used in combination with flying probe,in-circuit and functional test methods.3,4 Despite the benefits offered by AXI,new users sometimes struggle with its implementation due to a lack of experience and procedures on how to optimize the inspection process to achieve stated performance targets. Common concerns among this user group include high false failure rates and defect escape rates. Because AXI is a relatively new test technology,many users are unaware of best practice use-models and continuous improvement methodologies that can be used to stabilize the inspection process and attain targeted performance goals for both defect detection and false failure rates. This paper will demonstrate procedures,use-models and continuous improvement methodologies that AXI users should consider when establishing norms for their own operational practices. Like any manufacturing process,appropriate procedures and metrics must be put in place to attain performance goals. Once suitable operational procedures are in place,even new manufacturing technologies like AXI will perform within predictable and acceptable performance limits. The recommendations and best practices discussed in this paper are derived from the practical experiences of the authors in their direct work with AXI processes in volume production environments.

Three epoxy systems were evaluated for physical and optical properties. The three systems chosen for the study were selected on the basis of their optical clarity,color and chemistry. Three distinctly different chemistries were chosen,aromatic epoxy- amine cured. Aromatic epoxy- anhydride cured and cycloaliphatic epoxy- anhydride cured. All three systems remained optically clear and water-white after full cure. The three selected systems were tested for physical properties,adhesion and light transmission properties. Light transmission was measured after thermal andHumidity Exposure. Adhesion was measured afterHumidity Exposure only. Both of the epoxy-anhydride systems performed well in optical properties but poorer in adhesion as compared to the epoxy-amine system. The aromatic epoxy-amine system discolored badly during thermal exposure at 100 C. Data generated from this work will be used in selecting clear encapsulating materials for photonics applications. No single system offers optimal performance in all areas. The best compromise material is the aromatic epoxyanhydride system.

The purpose of this study is to understand the capability of both AOI and AXI machines and where the two could be combined to increase the inspection coverage,reduce the overall cycle time of the inspection process and provide the most cost effective solution.

Application of solder paste by using stencil-printing process is a commonly used method for high volume electronics circuits manufacturing. This process has proved to be the fastest and most cost-efficient. Unfortunately this method has shown its limitation for components with pitch smaller than 300 micron. For these components an alternative method is the tacky flux process. It takes place directly on the fine pitch component mounter equipped with flux-dipping unit. The process stages can be described as follows:
1. Pick up component;
2. Dip component bumps in the flux unit;
3. Place component on the substrate.
The expectation is that this assembly process will allow handling of components with bump pitches down to 100 micron. Therefore it can be extremely interesting for assembly of Flip Chips with eutectic bumps. When FCs with eutectic bumps are placed in solder paste,the position of most components is corrected during reflow,due to the self-alignment of the liquid solder. Likewise,when components with eutectic bumps are placed in flux,the position of most of them is also corrected,due to self-alignment,but the placement accuracy requirements have not been fully investigated. This article presents the research findings with reference to the relationship between placement accuracy and formation of solder joints for components with eutectic bumps placed in flux.

Many papers and articles are claiming that a majority of the defects detected after reflow are coming from the solder paste application process. However,very little real data seems to be available to support this claim. To investigate the paste process impact on defects after reflow,Nokia in Finland and Agilent Technologies decided to do a joint study. The study was designed to use a paste inspection system to measure paste volume directly after the paste application process and to use an automated X-ray inspection system to measure defects after reflow. The first part of the study was to correlate the paste and the X-ray systems to each other using a small number of PCAs. After this correlation study,one week of production volume was analyzed and more than 680,000 solder paste bricks and later solder joints were measured. In this sample,46 defects were detected and confirmed after reflow but,very surprisingly,none of those was detected by the paste inspection. Also very surprisingly,over 2,000 paste bricks had below 65% of nominal paste volume,which in normal production would have triggered a repair action,but none of these -- over 2,000 “defects” at paste inspection -- created a “defect” after reflow.

The control of moisture-sensitive devices (MSDs) prior to SMT reflow is a critical assembly issue that has a direct impact on final product reliability and customer satisfaction as well as manufacturing costs. The guidelines for storage and handling of MSDs are clearly defined in the IPC/JEDEC standard J-STD-033. However,the proper identification,tracking and calculations have always been very challenging to implement with manual procedures and they are prone to a high level of human errors. In most cases,implementation of an internal manual control procedure requires simplifications to the industry standard. This can have two possible effects:
1. When simplifying on the safe side,the user will end up baking parts that don’t really need it. This has serious implications in terms of lead solderability and solder joint reliability due to intermetallic growth. It also impacts material availability,which can affect production schedule,on-time delivery and inventory levels.
2. With other simplifications to the standard,a significant number of components that should have been baked will be assembled and reflowed. Although this may only happen to a small percentage of all the lots,it will typically involve a partial tray or reel containing many parts. Since MSDs are typically the most expensive components and there can be many such components on each PCB,even a small level of escape (less than 0.1% by component) can result in very high material costs and unacceptable levels of early life failures. It is now possible to use an automated control system that is both simple-to-use and can insure a very high level of control. The foremost objective of the system is to avoid assembling components that have exceeded their allowable limit. This is achieved by automatically tracking each reel or stack of trays from the time they are removed from their original dry bag until all parts are placed prior to reflow. The second objective is to minimize the number and duration of bake cycles by taking into account all applicable rules from the industry standard and ambient conditions,while providing real-time status and advance warnings.

As 0402 has become a common package for printed circuit board (PCB) assembly,research and development on mounting 0201 components is emerging as an important topic in the field of surface mount technology for PWB miniaturization. In this study,a test vehicle for 0201 packages was designed to investigate board design and assembly issues. Design of Experiment (DOE) was utilized,using the test vehicle,to explore the influence of key parameters in pad design,printing,pick-and-place,and reflow on the assembly process. These key parameters include printing parameters,mounting height or placement pressure,reflow ramping rate,soak time and peak temperature. The pad designs consist of rectangular pad shape,round pad shape and home-based pad shape. For each pad design,several different aperture openings on the stencil were included. The performance parameters from this experiment include solder paste height,solder paste volume and the number of post-reflow defects. By analyzing the DOE results,optimized pad designs and assembly process parameters were determined.

Like many other phrases carelessly thrown around by economists and business consultants,Return on Investment has become the overused acronym ROI,and has gained popularity so quickly that engineers more accustomed to dealing with SMT,VOC,PTH and ICT now use ROI as part of their everyday working language. But do those of us who use the acronym actually know what ROI really measures or captures in the manufacturing arena? Do we understand how can it be used to both justify and quantify investments in capital equipment? In fact,is ROI even an appropriate data point given the available manufacturing information flows?