Electroless nickel electroless palladium immersion gold (ENEPIG) surface finish for printed circuit board (PCB) has now become a key surface finish that is used for both tin-lead and lead-free solder assemblies. This paper presents the reliability of land grid array (LGA) component packages with 1156 pads assembled with tin-lead solder onto PCBs with an ENEPIG finish and then subjected to thermal cycling and then isothermal aging. To determine thermal cycle reliability,daisy-chain LGA1156 packages were used to enable the monitoring of solder joint failures. The assemblies,were built with a vapor phase reflow machine or using a rework station. Then,they were subjected to thermal cycling ranging from –55°Cto 125°C. Subsequent to the completion of two hundred thermal cycles,the assemblies were isothermally aged for 324hours at 125°C to determine the effect of isothermal aging on intermetallic formation and growth,which is one of the concerns for tin-lead solder assemblies. To determine the effect of exposure at temperatures higher than 125°C,the aged samples were subjected to 100 thermal shock cycles between –65°Cand150°C.A number of characterization methods were used to ensure the integrity of solder joints. These included nondestructive evaluation by X-ray,daisy-chain monitoring at thermal cycle/aging intervals,and destructive characterization by cross-sectioning. The cycled/aged samples were cross-sectioned and characterized by optical and scanning electron microscopy (SEM). Assembly processes and SEM photomicrographs showing damage progression and IMC/microstructural changes,as well as elemental analyses by x-ray energy dispersive spectroscopy (EDS),were also presented.

The stimulating impact of the automotive industry has sharpened focus on immersion tin (i-Sn) more than ever before. Immersion tin with its associated attributes,is well placed to fulfill the requirements of such a demanding application. In an environment dominated by reliability,the automotive market not only has very stringent specifications but also demands thorough qualification protocols. Qualification is ultimately a costly exercise. The good news is that i-Sn is already qualified by many tier one OSATs. The focus of this paper is to generate awareness of the key factors attributed to soldering i-Sn. Immersion tin is not suitable for wire bonding but ultimately suited for multiple soldering applications. The dominant topics of this paper will be IMC formations in relation to reflow cycles and the associated solderability performance. Under contamination free conditions,i-Sn can provide a solderable finish even after multiple reflow cycles. The reflow conditions employed in this paper are typical for lead free soldering environments and the i-Sn thicknesses are approximately 1 µm.

While there have been quite dramatic and evident improvements in almost every facet of manufacturing over the last several decades owing to the advent and mass adoption of computer automation and networking,there is one aspect of production that remains stubbornly unaffected. Massive databases track everything from orders,to inventory,to personnel. CAD systems allow for interactive and dynamic 3D rendering and testing,digital troubleshooting,and simulation and analysis prior to mass production. Yet,with all of this computational power and all of this networking capability,one element of production has remained thoroughly and firmly planted in the past. Nearly all manufacturing or assembly procedures are created,deployed,and stored using methodologies derived from a set of assumptions that ceased to be relevant fifty years ago. This set of assumptions,referred to below as the “Paper Paradigm” has been,and continues as the dominant paradigm for manufacturing procedures to this day. It is time for a new paradigm,one that accounts for the vastly different technological landscape of this era,one that provides a simple,efficient interface,deep traceability,and dynamic response to rapidly changing economic forces. There are of course,numerous different systems available to streamline the creation,deployment,and storage of ‘paperless’ work instructions but it is very important to understand that the simple absence of tactile paper,does not mean that a system has transcended the limitations of paper. Most procedures today are created using standard word processing tools,managed using file management systems and deployed using various different flavors of PDF. While the tools are slightly different than those available in decades’ past,there is no fundamental revolution in process and capability. A word processor is nothing more than a simple,logical extension of a typewriter. A file management system is nothing more than a virtual version of a folder overseen by a manager,and a PDF has the effect of turning a computer screen into nothing more than a sheet of paper. Regardless of the tool used for creation,regardless of the system used to manage files,and regardless of the mechanism of deployment,nearly all manufacturing instruction systems in place today conform to the same fundamental assertions as systems in place over one hundred years ago. The Paper Paradigm:
1.Procedures must be deployed to operators in a paper or paper analogue format.
2.Procedures can only provide a one-way flow of information from the document to the operator.
3. Procedures cannot react to changing circumstances.
4. Procedures cannot be interactive.
5. Procedure revision must be manually controlled.
This paper seeks to present an alternative. Instead of enhancing and improving on systems that became irrelevant with the invention of a database,instead of propping up an outdated,outmoded and inefficient system with incremental improvements; rewrite the paradigm. Change the underlying assertions to more accurately reflect our current technological capability. Instead of relying on evolutionary improvements,it is time for a revolution in manufacturing instructions. It is time to embrace a new paradigm.

Work instructions are time consuming to generate for engineers,often requiring regeneration from scratch to address very minor changes. They need to be produced in varying levels of detail,with varying guidelines,for multiple stations,operators and lines. Minor component,station or process changes –down to the modification of an individual BOM component –can cause headaches when attempting to maintain consistency across multiple work instructions that are touched by the change. The solution presented here improves efficiency and saves engineering time by making use of a database driven approach. Manufacturing details,component information,process guidelines,annotations,machine-specific data,and more can be stored in one central database. Any information stored in this single repository can then be modified quickly in one location and automatically propagate seamlessly throughout multiple work instructions. These can be instantly printed out or displayed on screens at appropriately affected stations with the simple click of a button,as opposed to regenerating from scratch,or going in and reviewing many documents to find and update with the change. An object-oriented based approach with information stored in one central location encapsulates all of the appropriate information at the level it should be presented. This allows clearer work instructions to be provided almost instantly –the moment any change is made to the database –while also maintaining consistency across all instances of the change in question.

Electronic assemblies use a large variety of polymer materials with different mechanical and thermal properties to provide protection in harsh usage environments. However,variability in the mechanical properties such as the coefficient of thermal expansion and elastic modulus effects the material selection process by introducing uncertainty to the long term impacts on the reliability of the electronics. Typically,the main reliability issue is solder joint fatigue which accounts for a large amount of failures in electronic components. Therefore,it is necessary to understand the effect of polymer encapsulations (coatings,pottings and underfills) on the solder joints when predicting reliability. It has been shown that there is a large reduction in fatigue life when tensile stresses exist in the solder due to the thermal expansion of the polymer encapsulation. The inclusion of tensile stress subjects solder joints to cyclic multiaxial stress state which is found to be more damaging than a conventional cyclic shear loading. Isolating the tensile stress component is necessary in order to understand its influence on a reduced fatigue life of microelectronic solder joints. Therefore,a unique specimen was constructed in order to subject Pb-free solder joints to the fluctuating tensile stress conditions. This paper presents the construction and validation of a thermo-mechanical tensile fatigue specimen. The thermal cycling range was matched with potting expansion properties in order to vary the magnitude of tensile stress imposed on solder joints. Solder joint geometries were designed with a scale factor that is relevant to BGAs and QFN solder joints while maintaining a simplified stress state. FEA modeling was performed to observe the stress-strain behavior of solder joints during thermal expansion for various potting material properties. The magnitude of axial stress in solder joints is shown to be dependent on both the coefficient of thermal expansion and modulus along with the peak temperature of thermal cycles. Results from thermal cycling of the specimen assist in correlating the magnitude of tensile stress experienced by solder joints due to the thermal expansion of potting material with various expansion properties and provides new insight into low cycle fatigue life of solder joints in electronic packages with encapsulations.

A study was performed to investigate,evaluate and qualify new reworkable underfill materials to be used primarily with ball grid arrays (BGAs),Leadless SMT devices,QFNs,connectors and passive devices to improve reliability. The supplier of the sole source,currently used underfill,has indicated they may discontinue its manufacture in the near future. The current underfill material is used on numerous circuit card assemblies (CCAs) at several sites and across multiple programs/business areas. In addition,it is used by several of our contract CCA suppliers. The study objectives include evaluation of material properties for down select,dispensability and rework evaluation for further down select,accelerated life testing for final selection and qualification; and process development to implement into production and at our CCA suppliers. The paper will describe the approach used,material property test results and general findings relative to process characteristics and rework ability.

It is well documented that Nano coatings on SMT stencils offer many benefits to those assembling PWBs. With reduced standard deviation and improved transfer efficiency nano coatings can provide,there is also a cost. As PWB assemblers work to justify the return on investment,one key question continues to arise. What is the durability or life of these coatings and what can be done in the print process to maximize the life of the coatings? This paper addresses durability of the coatings in relation to the number of print cycles and underside wipe cycles applied as well as materials used on the underside wipe process. Different parameters will be applied and data will be collected. The results of this study will be summarized to help those using or considering the use of these nano coatings to improve their print process and suggestions will be given to maximize the life of the coatings.

With each new generation,the complexity in the design of flip chip devices,as exemplified by thinner package stack-ups,larger device sizes,and multiple die configurations,is increasing significantly. This is creating new challenges in their surface mount manufacturing and their solder joint reliability. To improve surface mount solder joint reliability under mechanical stresses,such as those imposed under shock,drop,and vibration during transportation and end user handling,the use of polymeric materials to provide added reinforcement to the second level solder interconnects on flip chip ball grid arrays (FCBGA)and package-on-package(POP) solder joints has been proposed as a solution. Some of the common examples of such polymeric reinforcement applications in manufacturing include,but are not limited to,corner glue edge bonding,underfill (UF)application,and epoxy-containing solder pastes. However,as the solder joints’ pitch size and height decreases,control of the extent and uniformity of polymeric encapsulation of second level solder joints becomes more challenging. As a result,solder joint encapsulation materials (SJEM) have been developed to provide a better controlled and localized application process. Unlike other polymeric materials in use today,these SJEMs do not require an additional step for cure,since they are applied before the reflow soldering process step and cure during the reflow soldering process step. Based on past studies on polymer reinforced solder joints,mechanical shock performance generally improved with the application of the polymer reinforcement and was less sensitive to the polymeric material properties as long as the material has acceptable application,curing,adhesion and fracture strength properties. However,thermal cycling reliability is more sensitive to certain material properties of the reinforcing polymer. The glass transition temperature (Tg) and the coefficient of thermal expansion (CTE) are two such properties [1-2]. Materials with a low Tg and a high CTE often lead to accelerated solder joint failure from thermal fatigue. Therefore,the material properties of SJEM and the extent of material coverage on the solder joint both play important roles in optimizing solder joint reliability performance under mechanical and thermal conditions. In this paper,two SJEM material application methods,dispensing and dipping,will be studied for the extent and uniformity of their encapsulation of high density BGA solder joints. The solder joint mechanical shock and thermal cycling reliability from these two SJEM dispensing techniques,which correspond to different encapsulation coverage,will also be analyzed and discussed. From the assembly and reliability test results,both SJEM materials showed process feasibility to be applied,reflowed,and cured with SAC305 solder paste. Both SJEM application methods showed promising mechanical shock and temperature cycle reliability. These material scan be considered as a solution to replace underfills and corner glues for smaller,finer pitch components in the future.

Cleanliness level of PCBs is becoming more and more critical given component miniaturization,component density,and manufacturing practices that include no-clean solder flux. The reliability of high risk circuitry (Class 3-Class 1) assemblies requires clean assemblies with field protection using a conformal coating; including poly-para-xylene vapor deposited films. Residues from the manufacturing process limit the level of adhesion of conformal coating on a PCB. Conventional liquid coatings are limited in their uniformity under,around,and across the component,given the application method. The adhesion on hard to reach areas –one can argue-is not a major concern with liquid coatings,but an argument can be made for leadless components where the power and ground are in close proximity. Poly-para-xylene coating is truly a conformal coating that has the potential to penetrate crevices,bottom side of components,board surfaces,component surfaces and cavities present on the component. The purpose of this paper is to research the value of cleaning under Bottom Terminated Components before Conformal Coating. A QFN surface insulation resistance test vehicle,with sensors placed under the component termination will be used for this research. The designed experiment will study both cleaning and non-cleaning before poly-para-xylene coating. The response variables will be measured: 1.) Visual Inspection of Post Soldering Residues,2.) Site Specific Ion Chromatography and 3.) Surface Insulation Resistance using the IPC TM650 2.6.3.7 test method.

PCB design has evolved greatly in recent years becoming ever more complex. Board density is increasing,component standoff heights are decreasing and long term reliability requirements are greater than ever,particularly for Class III products. Given the quality and reliability demands for complex PCBs,manufacturing processes are qualified; that is,the PCB design,including component and solder paste/flux selection,material compatibility and process steps,must meet the long term reliability requirements demanded and quality standards desired. As a result,cleaning is becoming a mandatory step within the manufacturing process. Analytical tests are key elements to any qualification process. Through the IPC,numerous tests have been developed and have been added to industry standards. In particular,IPC-TM-650,method 2.6.3.7 or SIR (Surface Insulation Resistance) is frequently used regardless of the solder paste/flux type. Per the specification,this test can quantify the deleterious effects of fabrication,process or handling residues on SIR in the presence of moisture. Measuring changes in surface resistance is a standard way of testing cleanliness and long-term reliability of a test board or complete process assembly based on industry standards. There are numerous test vehicle options available to the industry for conducting SIR analysis. This study was designed to compare different SIR test vehicles,from a cleaning perspective,in order to determine which,test vehicle is tougher to clean and therefore challenge the cleaning process. The three (3) test vehicles selected were the IPC-B-52,IPC-B-36 and the SMTA Saber. Each test vehicle was populated with specific components. The authors chose to reflow the test vehicles with water soluble solder paste only,since the high activity flux in the water soluble paste would increase the chance of SIR failure if left partially cleaned. Multiple test vehicles were prepared. Cleanliness verification and validation was completed by visual inspection underneath all components as well as by performing SIR tests. All test vehicles were cleaned prior to reflow and ion chromatography was conducted on selected test vehicles initially to ensure they were free of any ionics. An inline cleaning process was used for all cleaning trials.