Some Ball Grid Array suppliers are migrating their sphere alloys from SAC305 (3% Ag) or 405 (4% Ag) to alloys with lower silver contents. There are a numerous perceived benefits to this move in terms of cost and performance,but process compatibility and reliability concerns have yet to be addressed.
Process compatibility concerns stem from the fact that the low-silver SAC replacement alloys have higher melting temperatures than SAC305,approximately 227°C as compared to 221°C. Certain families of electronic assemblies,such as consumer portables,are often heat-sensitive and are reflowed in the low end of the established lead-free peak temperature range,typically 230-235°C. The small temperature difference between the spheres’ melting temperature and the peak reflow temperature raises questions about the reliability of the solder joints that are formed under this tight thermal margin. These are similar to the concerns raised with the backward compatibility of SAC305/405 spheres with tin-lead solder processes. Some of the solutions identified in the lead-free ball/tin-lead paste scenario may apply to the low-silver ball/SAC305 paste combination,but they require review for their applicability with this new set of mixed metals.
A study has been undertaken to characterize the influence of alloy type and reflow parameters on low-silver SAC spheres assembled with backward compatible pastes and profiles. The DOE combines low-silver sphere materials with tin-lead and lead-free solders at different combinations of peak temperature and times above liquidus. Solder joint formation and reliability are assessed to provide a basis for developing practical reflow processing guidelines.

Portable Electronics devices are having more functionality but the size is getting smaller. What it means to SMT is to place more,smaller and ultra fine pitch devices on PC board. This makes SMT process capability the key measure to SMT quality. A number of the companies study the process capability at the time they evaluate or purchase the equipment,or at the time they design the product to fit the process capability. But process capability is changing over time. The process/machine was capable before may not be capable now. The paper focuses on process capability and process control. It suggests process capability study should be a routine rather than a one time work. The paper is based on the practices in our company’s manufacturing environment. For placement,the Cpk measurement was trialed on some of our lines. The measurement machine problem was analyzed and a proper measurement machine that fits the requirement was chosen. The Cpk result and product yield after proper calibration were very encouraging. For printing,a DOE was conducted based on the 0.4mm pitch BGA. The significant factors related to output of paste volume and paste deposit variation were found and an optimum setting combination was suggested to production. The process characterization has been proved to have a significant financial impact.

The European Union list of Substances of Very High Concern (SVHCs) published in the Registration,Evaluation,Authorization and Restriction of Chemicals (REACH) regulation,requires producers of Articles to provide a declaration regarding the presence of SVHCs to their customers within 45 days of request. To effectively communicate regulatory compliance,organizations require infrastructure and application development to incorporate 1752 and 9535 template standards.
Concurrently,a “green” movement is transitioning product design focus beyond regulatory and legislative compliance to
market-driven,eco-friendly electronics. This is causing many supply chain partners to be pulled in the direction of green leaders with a serious impact on organizations dependent upon the same sources of supply,design standards,and supply chain constituents.
This session will review today’s global manufacturing direction to eco-friendly products and its impact on electronic components and systems. It will explore compliance pressures and other very real concerns such as counterfeit parts,high reliability design,pursuit of Pb-free alternatives,supply volatility,and obsolescence. From component manufacturer and OEM/EMS perspectives,it will also discuss PCN/EOL,data transfer,and published standards that are de facto communication methods but vary significantly in practice. Given complex BOM configurations and the nature of specialized,outsourced supply chains this presents a greater threat to lifecycle performance. A framework will outline preparatory product lifecycle actions and leading approaches taken to address the Green product development movement.
This Executive Briefing discusses the results of two benchmark studies conducted in 2008 by Supply & Demand Chain Executive,in conjunction with IHS,“Benchmarking Green Supply Chain Priorities” and “Benchmarking Product Lifecycles for Green Performance.” Research of more than 300 companies demonstrates that Green is a disruptive market transition that has introduced supply chain volatility and unbalance without any apparent near term resolution.
This paper previews the most serious issues that impact supply chain stakeholders. Along with more comprehensive companion papers,it may serve as a guidebook to plan,prioritize and execute programs. Its central objective is to inform business leaders of both,direct and indirect,influences of Green marketplace behavior,and equip their organizations with strategies to maintain competitive performance,mitigate business risks,and ensure supply chain continuity.
It is a misconception that Green applies only to makers of eco-friendly products or those required to comply with regulations
like RoHS,REACH and EuP.* Although industries like aerospace and defense or communications may seem once-removed from the issues,they cannot ignore the supply chain changes that Green imposes,and they are arguably at greater risk to its influences.
The bottom line: Green is a mainstream marketplace shift,the influence of which ultimately impacts and changes supply and
demand dynamics. Regardless of regulatory compliance requirements,environmental product ambitions,or even short-term
competitive gains,those who chose to ignore its impact may face dire consequences and run the risk of being left behind.

RoHS exempt high reliability OEMs breathed a sign of relief for not having to go through the grind of revising their processes and material to be RoHS compliant. However,this was short lived because of supply chain disconnects in the availability of non-RoHS devices. Consumption,in terms of unit volume for Sn/Pb,is small compared to the volume going into the builds of Pb free consumer and commercial product. Many device manufacturers are discontinuing the Sn/Pb option on many part numbers (P/N) when unit volumes fall below a certain threshold.
Bills of materials are being transitioned to obsolete and legacy parts outside the control of the OEMs and at a rapid pace. The
life cycle for a military product generally takes over two years for the design and initial deployment,followed by a production life cycle of over 10 years and a repair/warranty cycle of 20 plus years. A redesign to include an alternate part number is no easy task due to redesign review,validation and reliability testing.
In addition,exempt OEMs are exposed to other problems caused by some manufacturers not changing P/Ns once the Sn/Pb is
obsolete. The end result too often is mixed reels of RoHS and non-RoHS product. Unfortunately,exempt OEMs are many times left with only one choice and that is Pb-free components. This is clearly not optimal due to some of the reliability concerns associated with Pb-free components. Reflow profiles,thermal stress,MSL,tin whiskers,tin pests,brittleness,voids and thermal mismatch are some of the reliability problems that can’t be ignored and can’t be managed in the absence of the specific Sn/Pb component.

Imagine that you were choosing a camera for your AOI system. Should you opt for a black and white camera or a color camera? This seems like a no-brainer. Most of us would go for a color camera. As humans,we take for granted that our world is in color. Most people see a brilliant color world effortlessly and without much thought to how the brain creates these color images. Cheap consumer color megapixel cameras are popping up everywhere from digital cameras,cell phones,and web cams. In the consumer space,color adds significant benefits to our everyday life from online interactions to saving our memories.
However,there are in fact hidden complexities in the choice of using color in the industrial space. Color cameras are typically slower than their monochrome counterparts. Color adds three times the information,which can slow down back-end processing. The quality of the image is highly dependent on the spectral characteristics of the illumination source. Furthermore,most AOI systems need to be able to resolve and measure small features accurately and reliably,and this resolution requirement can be at odds with how color cameras measure color attributes from the world. Even with the inclusion of a color camera in an AOI system,one must address how color can and should be used in AOI machines so that the system can identify defects and measure process attributes. Because of these and other considerations,it is not entirely obvious as to which camera system is best for a given AOI scenario.
There are significant benefits and pitfalls to using color in automated inspection of printed circuit board and the use of color must be thought through carefully. Over the last 10 years we have studied the science,the technology,and the application of color in AOI. In this paper we bring to light important issues about color that are surprisingly little known except to a select community of color scientists. We also show how these issues aid and detract from AOI inspection. Finally we discuss how even with the adoption of color hardware,software can make or break its overall benefits to AOI inspection.

The handheld wireless product market place demands products that are small,thin,low-cost and lightweight and improved user interfaces. In addition,the convergence of handheld wireless phones with palmtop computers and Internet appliances is accelerating the need for functional circuits designed with smallest,low-cost technologies.
The miniaturization of portable electronics and Mobile handsets is resulting in thin form factor cell phones,camera modules and Bluetooth packages. The consumer appeal for sleek phones is driving the need for thin PWB roadmaps for the handset. [1]
Qualification of thin PWBs (less than 0.8mm) require careful evaluation of PWB stackup for warpage,delamination and successful lead free reflow and rework. The paper presents the qualification testing of thin PWBs for warpage characteristics. X-sectional analysis,shear testing,thermal shock,temp. Humidity testing and drop test for long-term reliability.

The conversion to lead free Ball Grid Array (BGA) packages has raised several new assembly and reliability issues. One reliability concern becoming more prevalent is the increased propensity for pad cratering on Printed Circuit Boards (PCBs) [1,2].
Lead-free solder joints are stiffer than tin-lead solder joints,and lead-free compatible (Phenolic-cured) PCB dielectric materials are more brittle than the FR4 (dicy-cured) PCB materials typically used for eutectic assembly processes. These two factors,coupled with the higher peak reflow temperatures used for lead-free assemblies,could transfer more strain to the PCB dielectric structure,causing a cohesive failure underneath the BGA corner pads.
The likelihood of pad cratering occurring in any given assembly depends on several factors including,but not limited to,the BGA package size,construction and surface finish; and the PCB pad size,material and surface finish. Standard assembly level bend,shock and drop tests can be used to determine if the entire assembly can survive a given strain and strain-rate range without having any failures.
However,with these standard assembly-level tests,it is difficult to determine if the failures occurred due to an unusually weak PCB dielectric/PCB pad size or a stiffer BGA package. It is critical to have a standardized test method that can be used to characterize and rank-order different PCB dielectric materials and PCB pad sizes.
In this study,an easy-to-implement test method to quantify the propensity for pad cratering in different PCB materials is presented. Gage repeatability and reproducibility studies to fully develop the test method were performed. Several different design variables,such as PCB material,resin content,solder alloy,number of reflows,pad size and shape were studied with a range of material sets. The test method was refined to develop a comparative metric that can be used to rank-order different PCB materials and pad size combinations.

For many critical electronic applications,there is a need for dielectric systems that exhibit better electrical insulation
performance than epoxies and other conventional materials. In the production of advanced telecommunications,high-speed
electronic and microwave equipment as well as radomes and other products being developed today throughout the world,
manufacturers rely on materials such as Teflon®,cyanate esters,and cyanate ester/epoxy blends to meet their performance
requirements. However,these materials feature disadvantages that can make them costly and difficult to use as dielectrics in some of these demanding applications.
We have an active research program to develop novel new thermosetting polymers with low Dk/Df properties. This paper
focuses on the testing of one of these materials as a base resin for PWB multilayers. This new system may also have applications outside the scope of this study.

Two major trends in printed wiring boards electronics are applications that require higher operating frequency,often in the radio frequency range (GHz),and the use of lead free solder assembly. Material requirements for dielectric materials have become more stringent. Key characteristics for dielectric materials are low dielectric constant,low dielectric loss,high use temperature,and low moisture uptake. The use of engineering thermoplastics has been investigated as a means to enhance performance of thermoset resins. In particular,polyphenylene ether (PPE) exhibits excellent hydrolytic stability,low moisture absorption,extremely high glass transition temperature,outstanding electrical properties over a wide temperature and frequency range,and ease of flame retarding without the use of halogenated materials. Investigations on the use of engineering thermoplastics in thermoset resins have pointed out the complexities of the network molecular architecture. Indeed,a wide variety of network morphologies were obtained within the fully cured material. PPE telechelic macromers have been reported as a breakthrough in the search for materials that broadly enhanced performance of dielectric materials. Thus the use of PPE macromonomers as a co-reactant in epoxy resins resulted in extensive performance advantages. Indeed,the use of PPE macromoners in epoxy resins resulted in single-phase networks,exhibited an increase in glass transition temperatures (Tg),lower dielectric properties,lower moisture absorption,and increased toughness. Single-phase matrices were also obtained with cyanate esters that exhibited lower moisture absorption and increased toughness. Vinyl modified PPE macromers were used in resins cured via radical polymerization. These resins exhibited very low moisture absorption in addition to high Tg and very low dielectric properties. The advantages of PPE macromoners in enhancing key properties of various dielectric materials suggest utility in a variety of demanding electronic packaging applications.

The use of flexible circuit boards in the design and manufacture of electronic products has experienced a consistent and rapid growth over the last 15 years because their light weight and physical flexibility make it possible to combine electronics,packaging design,and styling to create exciting new consumer products. And as the capacity and pin density of electronic components has continued to increase,new demands are being created for flexible circuit boards. These new demands include the need for thinner copper on thinner flexible substrates with greater bending flexibility and durability.
The most common commercialized process today for the deposition of ultra-thin copper on flexible base materials is a vacuum sputtering process. In this process,there is a sputtered tie coat of chromium or other metals or alloys to improve the adhesion to the base,followed by sputtering of a thin layer,usually about 0.2 micron,of copper. Quite often the substrate is pre-treated with plasma to improve tie coat adhesion to the base material. This is often followed by the electro-deposition of copper to the desired final copper thickness. These products have been successful in the adhesiveless-copper-on-flexible substrate marketplace. However,the process is expensive because of the need for high capital cost vacuum deposition equipment,is energy intensive,requires the use of toxic metals,requires many processing steps,and is inherently single sided. In addition,the process requires additional processing steps beyond normal etching processes for the removal of the tie coat.
We are commercializing an innovative approach for metalizing flexible substrates. This new approach,which was developed
in the labs of SRI International (formerly Stanford Research Institute) is a non-vacuum process that eliminates the need for
expensive vacuum deposition,eliminates plasma treatment of base material,eliminates several expensive process steps normally associated with conventional copper coating techniques,and produces superior adhesion without the need for a tie coat. All of the process steps can be single or double sided,and have been implemented with a roll-to-roll manufacturing process. Flexible circuit materials made with this process can be used in most types of flexible circuit board manufacturing processes including subtractive and semi-additive methods. The copper deposited is ductile,and has good thickness tolerance. We have achieved outstanding adhesion to the base material along with good surface insulation resistance (SIR) and other pertinent properties. The process that has been implemented can produce coated copper with a thickness ranging from 0.1 micron to 18.0 micron. A variety of base materials have been studied with good results. These include polyimide,particle filled polyimide,liquid crystal polymers (LCP),polyesters,and composites. And the total process is inherently “greener” than existing materials and methods because of the elimination of most (99.95%) or all of the etched materials used in conventional subtractive and semi-additive processes today.