Large printed wiring assemblies (PWB) exceeding 7000 circuit nets create significant quality,cycle time and cost issues at structural test in the new product introduction (NPI) phase. Traditional in-circuit test and its requirement for expensive bed-of-nails (BoN) fixtures impose high tooling costs and long cycle times. While flying probers (FP) do not require test fixtures,thereby reducing those cost and time impediments,testing large board imposes extremely long test time and lower test coverage. We describe a “Flexible Fixturing System” which overcomes the cost and tooling cycle times inherent with traditional BoN fixtures while simultaneously providing the high throughput rates and test coverage of traditional in-circuit testers. Moreover,this is accomplished at an attractive capital cost.

This paper discusses the benefits and limitations of universal,low-pin count Automated Test Equipment for Printed Circuit
Assembly (PCA) testing utilizing the test access port (TAP) defined in IEEE Std. 1149.1. The test equipment under
consideration allows the application of a wide variety of JTAG/Boundary Scan connectivity and pseudo functional tests,ideal
for use as a desktop test system for prototype verification and production test. In particular,we will present ways of creating
test applications that utilize embedded test resources in the Unit Under Test (UUT) and tester channels provided by the ATE
in a compact and all-inclusive fashion. The paper will also discuss overall cost of test reductions achievable with such test
equipment.

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.

Since the electronics industry moved to lead-free solders that typically have a tin content of more than 95% there has been
concern about the possibility of circuit malfunctions due to whisker growth. It is now generally accepted that whisker growth is a response to compressive stress within the tin crystal and the challenge is to identify and eliminate or at least minimize the
processes that can generate such stress. Corrosion has been identified as one source of that stress and in this paper the
authors report a study directed at identifying the relationship between the extent of corrosion and the concomitant whisker
growth. Printed circuit coupons with an OSP finish were soldered with SAC305 solder using wave,reflow,and hand soldering methods with flux formulations typical of current commercial practice. These coupons,soldered but without components,were exposed to three environments for up to 3000 hours: 40°C/95%RH,60°C/90%RH and 85°C/85%RH. As well as recording the location of whiskers,their density,and length as a function of time,the extent of corrosion of the solder after 1000,2000 and 3000 hours was measured by cross-sectioning. The ultimate determinant of whether or not whiskers appeared was the environment to which the test pieces were exposed. The highest incidence (whiskers per unit area),fastest growth rate,and greatest length occurred on test pieces exposed to 85°C/85% RH. Whiskers occurred later,at a lower
incidence,and grew more slowly at 60°C/95% RH but even after 3000 hours no whiskers were detected on test pieces exposed to 40°C/95% RH. The incidence and growth rate of whiskers was found to vary with the soldering method and the type of flux. Whisker growth occurred earliest on the test pieces that had been wave soldered. Geometry was found to have an effect with the concavity created on the edges of traces by the etching process apparently acting to focus the compressive stress and accelerate whisker growth in that area. The authors relate these trends in whisker growth to observations of the concurrent corrosion of the solder which in turn is related to the type of flux used. A preliminary conclusion is that the likelihood of whisker growth occurring on lead-free assemblies soldered using no-clean technologies can be significantly reduced by using a flux which does not promote the sort of corrosion that can generate compressive stress in the solder.

The objective of this study is to evaluate conformal coatings for mitigation of tin whisker growth. The conformal coatings chosen for the experiment are acrylic,polyurethane and parylene. The coatings were applied in thicknesses ranging from 0.5 to 3.0 mils on 198 bright tin plated coupons with a base metal of either Copper C110 or Alloy 42. Prior to coating,light scratches were applied to a portion of the coupons,and a second fraction of the coupons were bent at 45° angles to provide sources of stress thought to be a possible initiating factor in tin whisker growth. The coupons have been subjected to an environment of 50°C with 50% relative humidity for over five years. Throughout the trial period,the samples were inspected by both optical and scanning electron microscopy for tin whisker formation and penetration out of the coatings by tin whiskers. Tin whiskers were observed on each coupon included in the test,with stressed regions of the bent samples demonstrating significantly higher tin whisker densities. In addition,the Alloy 42 base metal samples showed greater tin
whisker densities than the Copper C110 base metal samples. There were no observable instances of tin whisker penetration out of the coatings or tenting of the conformal coat materials for any of the non-stressed test coupons. The stressed coupons demonstrated tin whisker protrusion of the 1.0mil thick acrylic and polyurethane coatings for the Alloy 42 base metal samples. The greater thickness coatings (minimum of 2.0mils) did not demonstrate tenting or tin whisker protrusion. This paper will also include materials properties of the conformal coatings examined along with appropriate processing techniques in order to better understand the role of the coatings in tin whisker mitigation.

Counterfeiting is clearly a growing problem in many industries,including electronics,around the world. As the financial impact of counterfeiting has grown over the years,so has the attention that has been devoted to it by everyone from packaging,assembly,and test engineers to procurement and quality personnel. Today,many feel that counterfeiting is the number one issue that threatens the electronics supply chain.

•Background information
•Scope of the problem
–Anecdotal
–Study by International Chamber of Commerce
–Recent study US Dept of Commerce
•What to do about it ?
–“Findings” and “Best Practices”
•Types of strategies

Wave soldering is a mature manufacturing process that metallurgically joins component and PWB termination features by
passing them together across the flowing surface of a molten solder reservoir. During this exposure,copper from through holes,surface mount lands,and component leads,continually dissolves into the molten solder. Unless the solder in the reservoir is Regularly changed,the dissolved copper eventually reaches a point of saturation,and orthorhombic Cu6Sn5 crystals begin to precipitate out of the molten solder,causing it to become gritty and sluggish. Solder drawn from such a saturated wave solder pot can solidify into joints whose surface finish exhibits many needle like metallic protrusions. These protrusions are in fact orthorhombic Cu6Sn5 crystals. Recently,BAE Systems has determined that this same phenomenon is responsible for the formation of nearly invisible intermetallic microbridges between fine pitch surface mount component leads. They form when a solder bridge from a surface mount paste reflow operation is hand reworked with a soldering iron and copper desoldering braid. This paper documents several short circuit failures caused by this phenomenon,the investigation that identified the root cause of the problem,and the rework techniques that can be used to prevent its
occurrence.

Mechanical shock testing was conducted by Boeing Research and Technology (Seattle) for the NASA-DoD Lead-Free Electronics Solder Project. This project is follow-on to the Joint Council on Aging Aircraft/Joint Group on Pollution Prevention (JCAA/JG-PP) Lead-Free Solder Project which was the first group to test the reliability of lead-free solder joints against the requirements of the aerospace/military community.
Twenty one test vehicles were subjected to the shock test conditions (in four batches). The Shock Response Spectrum (SRS)
input was increased during the test after every 100 shock pulses in an effort to fail as many components as possible within the
time allotted for the test.
The solder joints on the components were electrically monitored using event detectors and any solder joint failures were recorded on a Lab view-based data collection system. The number of shocks required to fail a given component attached with SnPb solder was then compared to the number of shocks required to fail the same component attached with lead-free solder.
A complete modal analysis was conducted on one test vehicle using a laser vibrometer system which measured velocities,accelerations,and displacements at one hundred points. The laser vibrometer data was used to determine the frequencies of the major modes of the test vehicle and the shapes of the modes. In addition,laser vibrometer data collected during the mechanical shock test was used to calculate the strains generated (using custom software).
After completion of the testing,all of the test vehicles were visually inspected and cross sections were made. Broken component leads and other unwanted failure modes were documented.

This paper is an examination of the process feasibility,solder joint reliability,and materials/process compatibility of a dippable solder paste material for an area array component rework/repair process. The Ball Grid Array (BGA) components in this investigation were reworked according to typical production procedures and a new dipping procedure using the AirVac Onyx 29 BGA rework machine. The components were tested for thermal cycle solder joint reliability and flux process compatibility. The thermal cycle and flux process compatibility test results demonstrated that the dippable solder paste material and BGA rework process were acceptable for IPC Class 3 High Performance products.