Various forms of contamination on the surface of hydrocarbon ceramic dielectric PWBs have been observed following component population. Although contamination is occasionally observed on PWBs fabricated from other dielectric materials,the light color of hydrocarbon ceramic substrates increases the frequency of detection,and consequently increases the number of investigations into possible contamination causes and impacts to reliability. Three contamination types are evaluated: staining due to rework of gold plated surfaces,discoloration due to flux application,and the resulting anomalies due to the effects of multiple chemical processing steps. The causes of the anomalies,quantitative analysis of residues,and impacts to reliability for each of these contaminants are discussed.

All things corrode,and the rate of corrosion among electronics devices is accelerating. Electronic devices are being used in more places than ever before. They are finding more uses,they're more portable,and they're increasingly used in polluted areas. Worldwide industrialization has produced more sulfur,chlorine and nitrogen compounds that aggressively attack electronics. The initiatives to eliminate lead (Pb) in electronics reduced the ability for circuitry to resist corrosion. To replace thick tin-lead deposits more circuits employ thin,easily corroded surface finishes on the PCB,connectors,and component leads. There is a need for better prediction of service-life corrosion,yet there is a lack of adequate test methods. Environmental testing rarely progresses beyond thermal cycling or heat/humidity. Mixed flowing gas testing uses standardized pollutants as a stress to electronics,but has limited success in reproducing all corrosion failures. An elevated rate in the observation of one type of failure,termed creeping corrosion,motivated the electronics industry to review corrosion test methods. As part of the IPC 3-11g committee,a number of OEM's,EMS providers,PCB fabricators,material suppliers,universities,and testing laboratories joined forces to address the need for better corrosion prediction.
The project conducted experiments using environmental pollutants and various levels of exposure to moisture to form corrosion salts from copper circuitry. A main objective of the testing was to create a standardized method for inducing corrosion. Test results will show the ability to recreate creep corrosion at the participating laboratories. As a project summary,this paper will review the many attributes of a PCB surface finish,the ways that each finish can fail under environmental contamination,the mechanism of creeping corrosion,and new ways to interrupt the corrosion mechanism while preserving other surface finish attributes. The summary contained herein had been intended to include the latest corrosion results from the IPC 3-11g team; however,the testing was not complete by the time of publication. This review will detail the status of the team’s findings to date,provide references to newly collated data,and chart the team’s forward direction.

Electronics,especially mobile electronic items,are subjected to unintentional abuse by having various beverages spilled onto or into them. Ion Chromatography and emission spectroscopy were used to identify the common inorganic ions in various carbonated drinks,coffee,tea,milk,juices,beer,wine,hot chocolate and a well-known sports drink. Except for the carbonated drinks,the others were then intentionally spilled onto clean circuit boards,dried,extracted and re-analyzed. The results show that there is generally little change from the virgin materials using the IPC extraction method and thus a library of “usual suspects” can be accumulated for comparison purposes for electronic products that come back from the field.

Printing technologies provide a simple solution to build electronic circuits on low cost flexible substrates. Nanocomposites will play important role for developing advanced printable technology. Advanced printing is relatively new technology and need more characterization and optimization for practical applications. In the present paper,we examine the use of nanocomposites or materials in the area of printing technology. A variety of printable nanomaterials for electronic packaging have been developed. This includes nano capacitors and resistors as embedded passives,nano magnetic materials,multifunctional materials,etc. Nanocomposites can provide high capacitance densities,ranging from 5nf/inch2 to 25 nF/inch2,depending on composition,particle size and film thickness. The electrical properties of capacitors fabricated from BaTiO3-epoxy nanocomposites showed a stable capacitance and low loss over a temperature range from 25 0C to 100 0C. A variety of printable discrete resistors with different sheet resistances,ranging from 1 ohm to 120 Mohm,processed on large panels (19.5 inches x 24 inches) have been fabricated. Low resistivity nanocomposites,with volume resistivity in the range of 10-4 ohm-cm to 10-6 ohm-cm depending on composition,particle size,and loading can be used as conductive joints for high frequency and high density interconnect applications. Thermosetting polymers modified with ceramics can produce low k dielectrics with k value in the range between 5.41 and 3.59. Similarly,low loss dielectric materials can be produced form mixing epoxy with silica or other low loss fillers. Reliability of the nanocomposites was ascertained by IR-reflow,thermal cycling,pressure cooker test (PCT),and solder shock. Change in capacitance after 3X IR-reflow and after 1000 cycles of deep thermal cycling (DTC) between -55oC and 125oC was within 5%. Most of the nanocomposites in the test vehicle were stable after IR-reflow,PCT,and solder shock.

Following the implementation of WEEE legislation,there will be an increasing interest in adopting more sustainable manufacturing processes and materials as targets are increased,and must be achieved without a loss in performance. These innovations may well lead to alternative failure modes. This work studies the performance of specific favoured materials to qualify the failure mechanisms and the effective stress screening regimes,and hence put in place the underpinning work for developing a test method for characterising these materials.
Three systems are evaluated; thermoplastic printed circuit assemblies based on copper-clad polyetherimide,polymer thick film on PET,and direct write copper on PET,were assembled using electrically conductive adhesives and tested using damp heat,dry heat and thermal cycling. All combinations showed very good reliability during the arduous testing. Chip resistor components generally showed less than 5% failures due to increased joint resistance after 1000 hours at 85°C/85%RH or 1000 thermal cycles from –55°C to +125°C. Results from gull-wing SOIC components were less promising but current work is investigating assembly methods to improve reliability of these components. Results were found to be conductive adhesive dependent,but results show that if the right combination of materials is chosen,thermoplastic substrates can be reliable for a wide range of electronics applications. The thermoplastic substrate technology offers great flexibility,for example 3D manufacturing or using the housing as the circuit board are all feasible. The lower energy and cost of manufacture and the improved potential for recycling indicate the value of further work.

Printed Circuit Boards (PCB) and IC Substrates are the essential building blocks of electronics. As the technology moves rapidly into the future,the electronics industry faces issues with hot spots,solder joint stresses and Co-efficient of Thermal Expansion (CTE) mismatch in a PCB and IC substrates. The most popular material used in the PCB industry is glass fiber based composite material. It delivers great electrical properties but has minimal thermal and mechanical properties. As more functionality is required from a single device,the PCB is getting denser and has a very high heat load per unit area. Also,the speed of the electronics is becoming more critical. This means it is necessary to have the shortest electrical path between silicon and the PCB. This requires eliminating long wire bonds and moving to the Flip Chip types of packages. Flip chip type packages have more functionality and faster speed but also have very low CTE compare to traditional PCB material. Thus it is necessary to have a low CTE printed circuit board in order to keep solder joints intact with such low CTE packages. There are currently several materials available in the market to address thermal and CTE challenges but each material has its own
advantages and limitations. For example,heavy copper is often used for thermal management with a thermal conductivity up to 385 W/m.K. But it has a higher CTE (17 to 20 ppm/C) and high density (8.9 g/cc) and is not easy to drill for the smaller holes required for HDI PCBs. Thus,heavy copper has the ability to do thermal management at the sacrifice of weight,CTE and limited to non-HDI technologies. On other hand,CIC has ability to deliver lower CTE but again CIC is very heavy and hard to drill for smaller vias. Other material non woven Aramid can deliver low CTE but does not have good thermal conductivity. It also has a very high Z-axis expansion and is sensitive to the moisture absorption. Thus all above materials can address one issue but are limited in other areas.
The ideal solution for the challenges would be a material that has the ability to do thermal management,CTE control
and provide increase rigidity with no additional weight. Thus,it is necessary to think outside the box and find a material that can address multiple issues at once. If you look at carbon fiber,it has very unique thermal and mechanical (CTE and Stiffness) properties but it is not a dielectric fiber unlike glass fiber. If we manage to use carbon fiber along with the glass fiber,we can address electrical,thermal and mechanical aspect of the functionality required by the industry. This presentation will address: (1) Details of the carbon fiber,(2) Carbon fiber composite types and shapes necessary for the PCB and Substrate,(3) How to make the electrical conductivity of the carbon fiber a plus point as opposed to a hurdle,(4) What needs to be done to use it successfully,(5) How it can address thermal and CTE challenges,(6) Basic understanding of manufacturability: (6a) Compatibility with FR4,Polyimide and other materials,(6b) Effect of feature sizes,scaling,drilling,routing and (6c) DFM through CAM. If carbon fiber could be used as reinforcement material instead of glass fiber (only in few layers) it could bring following benefits to the circuit board:
•?Enable efficient conduction cooling
•?Create a thermal path from hot IC Chips to the frame or chassis
•?Allow the PCB to act as Heat Spreader and/or Heat sink
•?Control the CTE of a PCB to match with Components such as Ceramic BGA (CBGA),Ceramic Column Grid
Array (CCGA),Flip Chip (FC),and Chip on Board (COB) etc.
•?Deliver additional stiffness
•?Give a higher stiffness to weight ratio increasing shock and vibration reliability
•?Provide a thermal management material that does not add weight to the product

The increasing use of lead-free solder has introduced a new set of process parameters when setting up wave solder equipment for effective soldering. Determining the proper flow characteristics of the solder wave for adequate hole fill is an essential step in achieving a reliable process. A variety of solder waves exist in the industry; each with advantages and disadvantages when performing lead-free wave soldering. One way to ensure adequate hole-fill is by increasing contact time at the Chip Wave.
This paper will present recent work done on an innovative way of increasing contact time,hence improving hole fill for relatively challenging board design. This work also examines effect of various process parameters including effect of nitrogen on hole fill. In addition to the experimental work,comparison and discussion of many variations of solder waves including: “A” type waves,laminar waves,dual waves,inerted shrouds,tunnels,and non-inerted waves will be discussed in this paper. Information will be provided on improved utilization of old wave solder equipment and the correct selections of new equipment to optimize lead-free wave soldering.

Copper erosion from plated through holes (PTH) barrels in printed circuit boards (PCB) during both wave soldering and mini-pot rework can increase the risk of PTH reliability failures during field use. Alternative Alloys are being touted as one solution to reducing copper erosion. This study will compare the copper erosion resulting from use of one alternative alloy in wave soldering and mini-pot rework with the currently used SAC305 solder alloy. The PTH knee thickness will be measured on as-received boards,after wave soldering and after one 45 second cycle of mini-pot rework,and compared with the minimum PTH thickness necessary to meet product reliability requirements. The board test vehicle for this study has a thickness of 93 mils (2.362 mm) and its design is similar to a mid-size server board. The SnCuNiGe alternative alloy was chosen from the results of the previous investigation that compared 5 different alloys for the magnitude and variation in copper erosion from PTH knees when subjected to a mini-pot rework cycle,without prior wave soldering [1]. While the mean value of the copper erosion data sets from all 5
alloys did not show any technically significant difference,a particular alloy exhibited significantly lower variation in copper erosion data at the PTH knees. A comparison of this alloy with the SAC305 alloy for PTH knee copper erosion under actual wave solder and mini-pot rework process conditions was required.

Recent industry trends have focused around alternatives for the commonly used SAC305 or SAC405 alloys for wave soldering and solder fountain rework processes. Industry consortia are currently focusing efforts on researching other “alternative Pb-free alloys” which are available on the market today [1]. Financial and technical reasons are driving many process engineers to consider an alloy change. The financial motivation is based on the increasing costs of the high silver content SAC alloys. With the constant pressure of having to reduce manufacturing costs,an opportunity to switch to a lower cost alloy for wave soldering would be a welcomed change. The cost of some of the alternative Pb-free alloys can be as little as half that of SAC – an attractive option. The technical reason for moving away from using SAC alloys for wave soldering and solder fountain processes may be even more significant. The high copper (Cu) dissolution rates which result from using SAC305/405 alloys for solder fountain rework have been documented as a major concern for the electronics industry [2,3]. The SAC305/405 Cu dissolution rates are so high that there is barely enough time to perform a 1X rework and in most cases do not allow enough contact time to perform a 2X solder fountain rework without experiencing irreparable damage to the PCB. This process limitation is a concern,especially for high reliability,long life products which may require multiple reworks during their lifetime. This technical issue in turn creates further financial impact through increased product scrap. To help address this technical issue,the evaluation of alternative Pb-free alloys continues. Previous work on some of these alternative Pb-free alloys has shown the benefits of having Cu dissolution rates similar to that of the 63Sn-37Pb alloy [4].
The financial and technical reasons for making a change away from using SAC305 or SAC405 alloys at wave solder and solder fountain are indeed compelling. However,before making a change to an alternative Pb-free alloy,a number of questions need to be answered,such as,what alternative Pb-free alloy/s should be considered? Which alternative Pb-free alloy/s offers the best process yield? Which offer the best thermal and mechanical reliability? As these alternative Pb-free alloys are relatively new to the electronics industry and therefore data limited,further study of their reliability performance is essential. A number of comprehensive investigations studying the reliability of PTH structures assembled with SAC and select alternative Pb-free wave alloys have been published to date [1,5-8].
This paper,an evolution of earlier work on this topic,discusses results obtained from an internally designed PTH test vehicle constructed to evaluate three commercially available alternative Pb-free wave alloys (Sn-Cu-Ni,Sn-Ag-Cu-Bi and Sn-Cu-X) by comparing their performance to SAC405 and SnPb. The process performance of each alloy is discussed,including profile optimization and process yield analysis. Failure analyses are presented to identify and explain observed failure mechanisms. In addition,the thermal and mechanical reliability analysis of each alloy is discussed. The objective of this work is to select a suitable wave alloy replacement to SAC305/405 that provides similar if not better overall solder joint quality as well as thermal and mechanical reliability.

As designers strive to extract ever more performance from high speed transmission lines on FR4 substrates and their high speed derivatives,a requirement has arisen for a practical and robust “Go / No Go” test technique for loss to be deployed on the PCB production floor. The intent of this paper is to propose that RIE (Root Impulse Energy) testing is a practical and achievable test method. It is easily deployed and offers repeatable,reliable discrimination between PCBs fabricated with a range of varying base material loss characteristics.
Until recently digital signals on PCB transmission lines operated at sub gigabit data rates. Consequently,losses were safely ignored while characteristic impedance was the major transmission factor. Today loss is a major consideration when pushing the limits of transmission lines on PCB boards. A board may be designed to take advantage of the transmission capabilities of a high specification dielectric,but an inadvertent substitution of an inferior specification core or prepreg during the manufacturing cycle,which may easily go unnoticed,could be fatal to the electrical performance of the system.
This test is designed to give fabricators a first indication of a change in loss characteristic on a given transmission line structure / layer stackup. This change in characteristic loss may be due to a number of factors including incorrect material used in a stackup. It may also be used in conjunction with other techniques (more suited to lab / QA use) to flag the need to escalate problem builds for more detailed laboratory analysis.
The RIE method has been presented in previous papers and presentations [1]. This paper looks at some of the more practical implementations of deploying this method in a conventional production environment. TDRs from two manufacturers were used for the acquisition of results in this paper.