Drop Test: Lead-Free Board After Assembly and Rework

EMS007: "Of the two reworked joints that failed electrically, only the TQFP-144, the more compliant leaded component, showed signs of SnPb solder joint fatigue fracture. The failure of the other two components was due to pad cratering and severed traces. There was no correlation found between the number of reworks and the amount of electrical or mechanical failure since only three non-BGA components failed in the test. Most importantly, this sample set showed no difference in drop test performance between SnPb-reworked and non-reworked Pb-free solder joints for non-BGA components.

More data will be available upon completion of the NASA DoD Pb-free project"

Effects of cerium content on wettability, microstructure and mechanical properties of Sn-Ag-Ce solder alloys

Scopus: "We investigated the effects of adding small amounts of cerium (Ce) to low Ag content Sn solder (Sn-1.0 wt.%Ag) on melting temperature, microstructure, wettability and mechanical properties using differential scanning calorimeter, optical microscope, scanning electron microscope, energy dispersive X-ray spectroscopy, wetting balance tester, Vickers hardness tester and tensile tester assays. The addition of Ce had little influence on the melting behavior of Sn-1.0Ag solder, but improved its wettability, mechanical properties, and microstructure."

Noh, B.-I., Choi, J.-H., Yoon, J.-W., Jung, S.-B.

School of Advanced Materials Science and Engineering, Sungkyunkwan University, 300 Cheoncheon-dong, Jangan-gu, Suwon, Gyeonggi-do 440-746, Republic of Korea

The correlation between the liquid structure and the viscosity of Sn-Cu lead-free solders

Scopus: "The liquid structure of two lead-free solder Molten alloys, Sn-0.5Cu and Sn-1.8Cu (wt.%), has been examined using X-ray diffraction method. The main peak for liquid structure of Sn-0.5Cu is similar to that of pure Sn. A pre-peak has been found in the low Q part on the structure factor S(Q) of Sn-1.8Cu tested under 320C, but it disappeared finally when the testing temperature reached 350C.

The both viscosity was measured using a torsional oscillation viscometer. It was found that the anomalous variations of viscosity had a direct relation with the transition of the liquid structure, which is consonant with the results of high temperature X-ray diffraction. The microstructure of the solder matrixes as well as interfacial reaction between liquid solders and Cu substrates was also studied. The results show that particle-like Cu 6Sn5 intermetallic compounds (IMCs) emerge in Sn-1.8Cu solder matrix. The IMC layer at Sn-1.8Cu/Cu joint is thicker than that at Sn-0.5Cu/Cu interface. The correlative effect of liquid structure on phase evolution in the solder joints is analyzed"

Solder joint reliability in automotive applications: New assessment criteria through the use of EBSD

Scopus: "The transition to lead-free materials within the electronics industry has raised the question of solder joint reliability for automotive applications. Traditional analysis methods like shear testing and light microscopic cross section analysis do not offer explanations for different damage appearances of solder joints that seem to have same material properties, same production and aging history.

A better understanding of microstructural properties and changes will help to solve those questions. Therefore, EBSD is used to analyze the grain structure of solder joints in the as-soldered state and after different aging conditions. In this paper a test program that is just being carried out at the Volkswagen Lab is summarized and first results of texture analysis are presented."

Mechanical alloying synthesis and soldering microstructures of nanocrystalline Sn-3.5Ag-0.7Cu alloy powders

Scopus: "Nanocrystalline Sn-3.5Ag-0.7Cu alloy powders were successfully fabricated by mechanical alloying (MA). During MA, Sn, Ag and Cu powders were deformed, overlapped and cold-welded together to form lamellar composites. The lamellar composites were then transformed into equiaxial particles. The milled powders were composed of a supersaturated solid solution, named Sn(Ag, Cu), and intermetallic compounds (IMCs) of Ag3Sn and Cu6Sn5.

The average particle size (D4,3) and the melting point of the 60 h milled Sn-3.5Ag-0.7Cu powders were 19.9 μm, and 219 C, respectively. After melting the powders on a Cu substrate at 260 C, a dense solder was formed, consisting of a hypereutectic structure of oval shaped primary β-Sn and eutectic products of β-Sn, Cu6Sn5, and Ag3Sn. Meanwhile, the Ag3Sn laths at the solder/Cu6Sn5 layer interface and the coarse Cu6Sn5 plates in the solder were also detected"

Cyclic twin nucleation in tin-based solder alloys

Scopus: "The microstructure and Sn crystal orientations of lead-free solder alloys such as near-eutectic SnAgCu have a significant influence on the mechanical response of a solder joint to service conditions. Thus solidification processes were examined in SnAgCu solder joints. Distinct evidence of sixfold cyclic growth twinning of Sn during solidification from the melt was observed in Sn-Ag, SAC and Sn-Cu solders."

Three orientations of Sn grains, each having a common 〈1 0 0〉 direction, were found in each of these systems, though the morphologies of these cyclic twinned microstructures differed. Analysis of dendrite arm spacing in cyclically twined structures with a beach ball morphology implies that the common 〈1 0 0〉 axis intersects with the region of the nucleation event. Models are presented for two pseudo/metastable hexagonal unit cells based upon {1 0 1} or {3 0 1} twins that introduce the cyclic twinning structure at the nucleation stage. Formation of these hexagonal unit cells may be facilitated by the presence of alloy elements. Subsequent epitaxial growth of the tetragonal unit cell on this nucleus can account for all three types of morphologies observed in microstructures of Sn-rich solder alloys.

Binghampton University, US

In-service reliability assessment of solder interconnect in power electronics modules

Scopus: "Power electronic modules (PEMs) are widely used in aerospace and automotive applications where high reliability is essential. Solder joint fatigue is one of the major failure mechanisms in PEMs, a reliability assessment method for this failure mechanism is presented in this paper. Differing from the traditional reliability prediction methods, this approach allows the reliability performance of PEMs to be assessed in real time. Firstly, a compact thermo-mechanical model of the solder interconnect was constructed using both high-fidelity and reduced order computer modeling, it was then integrated with the lifetime model of the solder joint. Secondly, a real time compact electro-thermal model was developed using both experimental and computer modeling techniques, and was used to predict the temperatures of device junctions, interfaces etc. that cannot ordinarily be measured during service. Using the above two compact models the lifetime consumption of the solder interconnect in PEMs under service conditions can be calculated based on the linear damage rule. A demonstration of this reliability assessment method is also given at the end of this paper"

a School of Computing and Mathematical Sciences, University of Greenwich, 30 Park Row, London, United Kingdom

Effect of fillet shape on reliability

Scopus: "This paper presents a method mining the worst thermal fatigue life of solder joints on chip components used in vehicle electronics. Thermal fatigue life of crack initiation and propagation were calculated by using the finite element method. Statistical analysis of thermal fatigue life in the solder layer below the chip component was carried out. A sample of dispersed fatigue lives was generated by using the Monte Carlo analysis and response surface methodology (RSM). As a result, it was confirmed that the fatigue lives follow Weibull distribution. Furthermore, case study was also conducted to examine the effect of solder shape on thermal fatigue reliability. It was confirmed that there is the complex interaction between each shape factor of the solder joint. The fatigue life in solder fillet drops when a crack propagates into a fillet of solder. It means that the shape of solder joints should be designed to control the failure mode. In order to study the possible cases of fillet failure in mass product, the boundaries of normal failure cases and failure cases for the combination of shape factors was estimated."

Semiconductor Industry Leaders Form DA5 Consortium to Explore Lead Free Solutions

EMAsiaMag.com: "Bosch (Division Automotive Electronics), Freescale Semiconductor, Infineon Technologies, NXP Semiconductors and STMicroelectronics announced that they have formed a consortium to jointly investigate and standardize the acceptance of alternatives for high-lead solder for attaching die to semiconductor packages during manufacturing. The five company consortium is known as the DA5 (Die Attach 5).

For environmental reasons, the semiconductor industry is making every effort to eliminate high-lead solder, where feasible. However, there is no single identified lead free solution for all applications and there is no expectation of a substitute for a high-lead solder die attach before 2014. Any solution will require substitute material development and evaluation, internal semiconductor process and product qualification, and semiconductor production conversion to guarantee product reliability.

By jointly developing and qualifying an alternative, the DA5 consortium aims to reduce the qualification time needed by its customers and provide lead free and environmentally friendly solutions as quickly as possible"

Lead Free Initiatives Expand Horizons for Selective Soldering Technology: Frost & Sullivan | EMAsiaMag.com

EMAsiaMag.com: "Selective soldering (using nozzles) is being increasingly preferred to traditional wave (using pallets) and hand soldering techniques due to the enhanced capabilities in terms of cost, defect reduction, solder quality, and improved throughput. Lead free soldering has enabled selective soldering technology to gain more prominence and wider adoption"

New analysis from Frost & Sullivan finds that the capabilities offered by selective soldering technology over its competing solutions including hand or wave in terms of precision, quality and cost are key driving factors for accurate soldering of double-sided PCBs and high density, mixed technology boards.

"The automotive segment has been a vital factor in driving innovations in the selective soldering sector," notes Technical Insights Industry Analyst Kasthuri Jagadeesan. "Moreover, as mission critical applications such as military/defense and homeland security require highly reliable electronic assemblies, selective soldering has proved to be an excellent alternative to wave and hand soldering."

Although wave soldering is a traditional technology, the element of competition with selective soldering still exists. Some of the applications still rely on the dexterity of the hand; thus, it is difficult to completely replace hand soldering. Press-fit and pin-in-paste are other competing technologies for selective soldering.

HDPUG Issues Lead-Free Assembly Guidelines

PCB007: "Although successful so far, the strategy to defer changing to lead-free solder processes is increasingly being challenged by the diminishing availability of compatible SnPb finished/balled components. Component manufacturers responding to high volume lead-free product demand from the consumer markets, continue to terminate lead-containing product lines as they become cost prohibitive to supply. This leaves manufacturers of RoHS exempt equipment with a major dilemma on whether to procure components on a lifetime buy basis, post process components (e.g. lead solder dipping, BGA reballing) or adopt lead-free components and solder in their products."

With this scenario in mind, HDPUG has produced an updated lead-free guideline which focuses on the specific issues that face producers of products with high reliability and extended service life expectations. Project leader Thilo Sack, from Celestica, Inc., explains, "The perception exists that since lead-free has largely been implemented successfully in consumer applications that there should be no issues in transitioning those products still making use of the exemption. The aim of this revised lead-free guideline is to raise awareness and bring attention to the outstanding issues that still exist in the supply chain from the learning to date which will challenge the easy transition of currently exempt products to lead-free."

Lead-free Guideline ($300)

Alternative Alloy Study for Hole Fill and Copper Dissolution

High Density Packaging User Group International, Inc.: "Alternative Alloy Study for Hole Fill and Copper Dissolution
in Definition Project
Idea/Definition Information
Actual Project Stage: Idea and Definition
Project Category: Lead-Free
Start Date: 04/01/2009
Estimated Completion Date of Current Stage: 12/31/2010
Project Leader Company: Nihon Superior
Background

•Erosion of lands and traces due to copper dissolution is one of the key issues in lead-free assembly.
•Copper dissolution tends to occur especially in wave soldering and reworking of through-hole joints.
•Many of the alternative alloys that provide low Cu dissolution may require longer dwell times to achieve hole-fill."

Effects of Ni addition to high-lead solders on the growth of Cu 3Sn and micro voids

Scopus: "The results of this study can be summarized as below: (1) Minor Ni addition to high-lead solder can't retard Cu 3Sn thickness. However, the Ni addition to lead-free solder can retard Cu3Sn. (2) The Sn flux from the solder towards the Cu substrate would be reduced by thick Cu6Sn5. The shrinkage of Cu3Sn attribute to the decrease of Sn flux. (3) Ni retards the Cu3Sn growth through Cu6Sn5. (4) Micro voids formed after aging at 160 'C for more than 500 h in 10Sn90Pb-xNi and 5Sn95Pb-xNi solders."

Enhancing mechanical response of a 96.5Sn-3.0Ag-0.5Cu solder using energy efficient microwave assisted sintering route

Scopus "In the present study, the effects of conventional sintering and two-directional microwave assisted rapid sintering on the microstructure and tensile properties of a commercial lead-free solder (96.5Sn-3.0Ag-0.5Cu) are investigated. Conventional sintering was conducted on solder samples in an inert Argon atmosphere, whilst microwave sintering was carried out on the samples under ambient conditions.

Two sintering temperatures of 150'C and 210'C were investigated. Microwave sintered samples exhibited lower porosity and more refined matrix grain size. Tensile results of microwave sintered samples also revealed superior strength (0.2% YS and UTS) when compared to conventionally sintered samples. Furthermore, results showed that samples microwave sintered at 210'C yielded the best combination of mechanical properties"

Effect of sub-micron alumina particulates on the properties of A Sn-0.7Cu lead-free solder alloy

Scopus: "Sn-0.7Cu lead-free solder alloy reinforced with sub-micron size alumina particulates in different volume percentage was synthesized using powder metallurgy technique incorporated with microwave sintering. Following synthesis, the extruded materials were characterized in terms of physical and mechanical properties. The density values of the composite solder materials were found to decrease with an increase in volume percentage of alumina particulates. The results of room temperature tensile test revealed that yield stress and ultimate tensile stress of the composite solder materials improved with the addition of alumina particulates. Particular emphasis is placed to interrelate the effect of volume fraction of sub-micron size alumina particulate added in the Sn-0.7Cu alloy with the physical and tensile properties of the resultant composite solder materials."

Zhong, X.L.a , Nai, S.M.L.b , Gupta, M.a

a Department of Mechanical Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117576, Singapore

b Minerals, Metals and Materials Technology Centre, National University of Singapore, 9 Engineering Drive 1, Singapore 117576, Singapore

Properties of new nano-structured particles reinforced lead-free composite solders

Scopus: "In order to solve the coarsening problem of reinforcing particles in fabrication of traditional composite solders and enhance the properties of lead-free composite solders, the eutectic Sn-3.5Ag and Sn-3.0Ag-0.5Cu were selected as solder matrix, and three different nano-sized polyhedral oligomeric silsesquioxane (POSS) particulates were used as reinforcing particles to form composite solders. The spreadability properties, mechanical performance, and creep rupture lives of solder matrix and their new composite solders with different mass fractions were studied."

The experimental results indicate that the new composite solders and their joints show better wettability, mechanical properties, as well as longer creep rupture lives than those of the solder matrix. Besides, Sn-Ag-Cu composite solder joints exhibit better properties compared with SnAg composite solder joints.

College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124, China

Creep and thermomechanical fatigue properties of in situ Cu6Sn5 reinforced lead-free composite solder

Scopus: "In this research, a composite solder, which consisted of the Sn-3.5Ag eutectic solder matrix and Cu6Sn5 intermetallic compounds (IMCs) as reinforcements, was prepared by in situ method. Cu and Sn metallic particles were added into the molten Sn-3.5Ag eutectic solder to form Cu6Sn5 reinforcements in solder matrix. After rolling, the Cu6Sn5 IMCs are crushed into fine particles and distributed uniformly in the composite solder.

The creep and thermomechanical fatigue (TMF) properties of the Sn-3.5Ag eutectic solder and its in situ Cu6Sn5 reinforced composite solder joints were successively investigated. The experimental results showed that the in situ Cu6Sn5 reinforced composite solder joint exhibited better steady-state creep strain rate, lesser TMF damages and higher residual shear strengths after different number of TMF cycles as compared to the Sn-3.5Ag eutectic solder joint. These indicated that the in situ Cu6Sn5 reinforced composite solder possessed excellent creep resistance and TMF properties. Besides, the fracture mode of the in situ Cu6Sn5 reinforced composite solder joint and the role of the in situ Cu6Sn5 reinforcing particles were analyzed."

Beijing University of Technology, 100 Ping Le Yuan, Chaoyang District, 100124 Beijing, China

Ni Zn alloy layer for BGA SAC ball - high reliability

Factiva: "A semiconductor device includes a substrate, a metal layer, an alloy layer and a Sn--Ag--Cu-based solder ball. The metal layer is configured to be formed on the substrate. The alloy layer is configured to be formed on the metal layer. The Sn--Ag--Cu-based solder ball is configured to be placed on the alloy layer. The alloy layer includes Ni and Zn as essential elements"

Kester Appoints New European Sales Manager

EMSNow: "Kester is pleased to announce the appointment of Michael Fullbrecht as European Sales Manager. Michael, formerly the Global Key Account Manager for the electronics assembly business unit at Henkel for more than 10 years, has been appointed to the new position at Kester, as part of the company's strategy to expand their European sales operation.

Michael will be responsible for expanding Kester's range of soldering and solder material products in Europe by maintaining and developing business to direct accounts and distribution in industries including electronics assembly, industrial, solar, communications and automotive. Michael will also be responsible for managing and growing Kester's European Sales force and Customer Service department. Kester's core product range meets the Siemens standard and Michael will also develop sales activities in Russia and Africa."

SMTA China announces winners of the 2010 Annual Awards

EMSNow: "David Hu, Technical Manager of Indium Corporation, was awarded Individual Member of the Year. David has been a very active member and has provided much support over the years to both the conference and training for SMTA China and also served as a course instructor of SMTA Engineer Certification Program in China."

PCB007 Online Magazine was named Media Sponsor of the Year for providing tremendous support throughout the SMTA China conferences, annual reception with online interviewing and promotion of SMTA China.

Henkel’s Multicore LF620 Lead-Free Solder Paste Sets the New Benchmark for the Lead-Free Era

Factiva: "This latest product from the global materials leader is a no-clean, halide-free, Pb-free solder paste that has a broad process window for printing, reflow and humidity resistance. In fact, the rigorous engineering at the foundation of Multicore LF620 ensures its consistent print performance with minimal hot slump even in regions with temperatures of 30-degreeC (86-degreeF) or more and relative humidity (RH) upwards of 80%. This makes Multicore LF620 well-suited for electronics firms that wish to use a single material for their worldwide operations, as its performance is unfailing regardless of extreme climate changes."

Imbedding components for increased reliability - Advanced Packaging

Advanced Packaging: "The testing of the two test vehicles has demonstrated that imbedding components and die is a robust packaging technology for use in products that must operate in harsh environments. The two test vehicles discussed in this paper have proven that the design guidelines, materials, and process parameters used to manufacture imbedded package assemblies are capable of withstanding temperature, humidity, and shock stresses."

Test Vehicle 1 (daisy-chain sample) survived over 3000 cycles of thermal shock exposure before a failure occurred. Test Vehicle 2 (mixed-signal prototype) was bench tested to meet and exceed legacy product performance specifications in order to qualify the prototypes as flight hardware. Lastly, a successful flight test in October of 2007 was paramount in demonstrating imbedded component packaging technologies’ ability to meet form, fit, and function requirements in a miniaturized robust package.

*The packaging technology described here is registered by STI as Imbedded Component/Die Technology (IC/DT).4

Transient liquid-phase sintering (TLPS) materials offer alternative to lead-free solder for power semiconductors

Indium Corporation: "Indium Corporation announces a joint marketing and technical support agreement for high-temperature Pb-free electronics assembly materials patented and manufactured by Ormet Circuits.

An agreement between Indium Corpoation and Ormet Circuits has resulted in a line of high-temperature, lead-free assembly materials for power semiconductor and semiconductor packaging applications.

When lead-free is a requirement, the established solution is the gold-tin (AuSn) eutectic alloy high-temperature solder. Transient liquid phase sintering (TLPS) materials offer an alternative technology to solder, and provide many of the assembly process advantages of a low-melting lead-free solder, combined with high-temperature joint stability."

Christopher Associates' Jasbir Bath to Moderate Low Silver Alloys Meeting at IPC APEX

Christopher Associates: "Christopher Associates announces that Jasbir Bath, Consulting Engineer with Christopher Associates/Koki Solder, will moderate Session S23 ..."

Press release

Global consumption of tin/lead vs lead free Solder

evertiq.com :: SMT & Inspection - Global consumption of tin/lead vs lead free Solder: "Director of Market Research at US based electronics industry trade organization IPC, last week held a session at the annual IPC Apex Expo, which Evertiq attended. One of the key topics included the global consumption of tin-lead versus lead free electronics."

The global solder industry has responded rapidly to the demand for lead free solder. Worldwide consumption of lead free solder was by the end of 2009 67%. China is the largest solder consumer in the world, followed by the United States. China is also the largest consumer of lead free solder. 81% of China's total solder consumption is lead free, while 19% still remains leaded.

All Asian countries together consumes in total 76% lead free solder. Japan consumes 76% lead free and Europe consumes 54% lead free solder.

The United States still only consumes 39% lead free solder. One of the main explanations for this is that a large proportion of electronics produced in the US is within the military segment. Lead free solder is less common in this segment.

Future Challenges of Lead-Free Rework: The Main Culprits Are High Thermal Mass and Product Miniaturisation

Surface Mount Technology: "That being said, readers should not get too comfortable based on this optimistic viewpoint of the history of lead-free rework. Although the industry has come a long way over a short period of time, the one caveat is that many of these challenges and solutions have been based on reworking smaller, low- to medium-complexity type products.

The majority of the focus over the next 2–3 years will be on implementing solutions for high-complexity, high-thermal-mass products, in preparation for the yet-to-be-finalized 2014 RoHS legislation."

MEPs remain divided on RoHS recast proposal

Chemical Watch: "Members of the European Parliament’s environment committee remain split over proposals to revise the Directive on the restrictions of hazardous substance (RoHS) in electrical and electronic equipment, making it increasingly unlikely that the committee will come to a consensus in time for a vote on the issue at the beginning of May. During the first discussion since MEPs tabled amendments at the end of March to rapporteur Jill Evans’..."

Update of IPC J-STD-609 Provides Greater Delineation of Lead-free Solders for Marking and Labeling - Surface Mount Technology

Surface Mount Technology: "Since the original release of J-STD-609 in July 2007, many new solder alloys have entered the market as lead-free technology matures. Companies like HP were witnessing how different component suppliers using the same (new) BGA ball alloy were selecting two different “e-codes” to mark their components. To address the confusion in categorizing the new alloys, Dr. Gregory Henshall, environmental program manager for HP’s Enterprise Servers, Storage and Networking Division, took an active role on the combined working group of IPC and JEDEC to pursue the A revision of J-STD-609."

“Confusion adds time and cost to the manufacture of printed circuit assemblies and also increases the chance for errors in material usage,” says Henshall. “The revisions made to the standard resolve this confusion, and include examples for many common alloys.”

J-STD-609A provides explicit guidance on the marking and labeling of components and PCBs using the wide range of solder alloys now available in the market. Specifically, the standard enables clear identification of assemblies with lead-containing or lead-free solder; components that have lead-containing or lead-free second-level interconnect terminal finishes and materials; base materials used in PCB construction, including halogen-free resin; surface finishes; and conformal coatings. In addition, the standard prescribes the maximum component temperature that should not be exceeded during assembly or rework processing.

IPC Updates Requirements for Soldered Assemblies

EMS007: "IPC - Association Connecting Electronics Industries has released the E revision of IPC J-STD-001, Requirements for Soldered Electrical and Electronic Assemblies. Recognized worldwide as the sole industry-consensus standard for soldering processes and materials, IPC J-STD-001E encompasses advanced technologies and provides new and updated criteria for all three classes of construction, as well as expanded support for lead-free manufacturing."

The product of a four and a half year revision process involving more than 3500 meeting hours from dedicated volunteers in the United States, Asia and Europe, as well as countless hours of industry-wide review through the consensus-building balloting process, IPC J-STD-001E contains new, expanded, updated and consolidated soldering criteria. Some of the significant changes are: New hole-fill criteria for Classes 1 and 2, new SMT termination criteria (flattened post/nail-head), expanded area array (non-collapsible balls and column grid array), expanded staking and adhesive criteria for bonding of through-hole and SMT components to PCBs, consolidated thermal management criteria and consolidated lead placement and soldering criteria for each terminal type

iNEMI Roadmap: R&D in Printing, Dispense

Surface Mount Technology: "As PCBs become more complex, the challenges for printing and dispensing technologies grow. Miniaturization, functional densification, and integration are driving 01005, 0201, finer pitch (0.3-0.4 mm) QFPs and SMT connectors, finer pitch (0.3-0.4mm) CSPs, flip chips and chip on board (COB) usage, as well as tighter spacing (<10 mil) between components. The increase in frequency and in the range of component sizes assembled on a single board adds to these hurdles."

The widening range of required paste volumes deposited on mixed-technology assemblies is pushing traditional stencil design rules to their limit. Further, there is a need for stencil, printing, and materials technologies advances to increase deposit consistency.

These changes require greater accuracy and control with stencil printing and new dispensing and patterning capabilities, especially when non-planar surfaces are introduced. This is an area to focus R&D efforts to ensure that SMT materials, processes, and equipment keep pace with the ever-increasing complexity in PCBs.