PCB Surface Research Articles

Failure Analysis on Soldered Ball Grid Arrays: Part I

Abstract This article is the first in a two-part series analyzing solder connection failures between BGA packages and PCB assemblies. Part I examines failures attributed to oxygen intrusion during reflow, underetched solder resist, and solder paste printing problems. In the latter case, X-ray inspection revealed no abnormalities other than a variation in ball size. To get to the root cause, the corpus of the BGA was progressively ground away, leaving only the balls and an unobstructed view of the PCB surface. A description of the process, supported by detailed images, is included in the article. In Part II, scheduled for the May 2017 issue of EDFA, the author delves deeper into the analysis of voids and presents an alternate FA approach that involves grinding away much of the PCB.

Reliability Analysis of Lead-Free Solder Joints with Solder Doping on Harsh Environment

Abstract This paper investigates the effect of long term isothermal aging and thermal cycling on the reliability of lead-free solder mixes with different solder compositions, PCB surface finishes, and isothermal aging conditions. A variety of surface mount components are considered, including ball grid arrays (BGAs), quad flat no-lead packages (QFNs) and 2512 Surface Mount Resistors (SMRs). 12 lead-free solder pastes are tested; for BGA packages these are reflowed with lead-free solder spheres of SAC105, SAC305 and matched doped solder spheres (“matched” solder paste and sphere composition). Three surface finishes are tested: Organic Solderability Preservative (OSP), Immersion Silver (ImAg), and Electroless Nickel Immersion Gold (ENIG). All test components are subjected to isothermal aging at 125°C for 0 or 12 months, followed by accelerated thermal cycle testing from −40°C to 125°C. Data from the first 1500 cycles is presented here, with a focus on the effect of surface finish on package reliability. Current results demonstrate that the choice of surface finish has a strong effect on reliability. However, different solder materials appear to show different reliability trends with respect to the surface finishes, and the reliability trends of BGA and SMR packages also diverge.

Evaluating the Effect of SMT Material & Process Variables on Voiding Under QFNs

Abstract Voiding under bottom terminated components (BTCs), such as quad-flat no-lead (QFN) components, is a problem which many circuit board assembly houses face on a daily basis. Such components have become very popular in circuit board assembly due to many of their benefits, including their small form factor, excellent thermal and electrical performance, easy PCB trace routing, and reduced lead inductance. Outgassing of flux in the solder paste used to attach QFNs to the PCB during reflow causes voiding under the components, as the gasses cannot escape because there is virtually no standoff under the QFNs. Voiding can have several serious effects on the performance of QFNs including reduced mechanical strength of the solder joint and hot spots under the QFN thermal pad because the voids do not conduct heat well. There are many process methods which are utilized in an attempt to mitigate the voiding issue, such as windowpane stencil designs and reflow profile. In this study, we will evaluate the effect of several other variables on voiding under QFNs, including solder paste powder mesh size, PCB surface metallization, and the reflow environment.

Enhancing tumor penetration and targeting using size-minimized and zwitterionic nanomedicines

We report a strategy to significantly improve tumor penetration of nanomedicines by using size-minimized and zwitterionic nanocarriers. We synthesized a series of 21-arm star block copolymers with the hydrodynamic diameter of 10–40nm and conjugated doxorubicin to the copolymers through pH-sensitive acylhydrazone linkages. The zwitterionic poly(carboxybetaine) (PCB), nonionic polyethylene glycol (PEG) and phenylboronic acid-incorporated PCB were selected as the peripherial hydrophilic blocks of the copolymers, respectively. We demonstrated that the size-minimized multiarm copolymer with PCB surface showed stronger tumor permeability when compared to the copolymers with PEG surface or larger size. The drug-conjugated multiarm copolymer that has the longest blood circulation time did not achieve the highest tumor accumulation. The incorporation of phenylboronic acid group into the peripherial block of the drug-conjugated multiarm copolymer significantly enhanced their cytotoxicity, cellular uptake, tumor accumulation, tumor permeability and antitumor activity.

Effects of PCB surface finishes on the Mechanical and Electrical Reliabilities of Sn-0.7Cu Pb-free Solder Bump

Effects of PCB surface finishes on the Mechanical and Electrical Reliabilities of Sn-0.7Cu Pb-free Solder Bump

The PCB Surface Defect Detection System Based on GPU Acceleration

Defective products are unavoidable in printed circuit board production process, so rapid detection and identificationmethods are badly in need of. PCB surface defect detection including a series of processing such as surface imagecapture, mixed noise filtering,images registering and so on, so it takes a lot of CPU time. To improve detection speed, based on GPU parallel computing platform, we designed a reasonable parallel processing system for PCB defect detectionto meet the need of real-time requirements of a production line. Experimental results show that parallel image processing algorithms based on GPU can achieve good results compared to the CPU-based serial algorithm (with speed up ratio up to8.34 in this paper),providing a new approachfor rapid detection of PCB surface defect.

플라즈마 유기막과 OSP PCB 표면처리의 Sn-Ag-Cu 솔더 접합 특성 비교

본 연구에서는 친환경적이고, 보관수명이 1년 이상이며, 부식특성이 좋은 플라즈마 유기막 표면처리에 대한 솔더링 특성을 기존 표면처리법인 OSP와 비교하였다. 플라즈마 표면처리는 할로겐계 전구체를 사용하여 CVD 방법으로 증착하였고, 증착두께는 20 nm이었다. 본 연구에서 사용된 솔더 조성은 Sn-3.0 wt%Ag-0.5 wt%Cu이었다. 염수분무시험에서 플라즈마 표면처리 유기막은 OSP보다 우수한 부식 저항성을 나타내었다. 멀티리플로우 조건에서 플라즈마 표면처리는 OSP보다 우수한 솔더 퍼짐성을 나타내었다. 솔더링 후 단면 미세조직을 분석한 결과, 플라즈마 표면처리와 OSP시편 모두 유사한 금속간화합물층 두께 및 형상을 갖고 있었다. 플라즈마 표면처리와 OSP 모두 유사한 접합강도를 가지고 있었다. Plasma organic thin film for PCB surface finish is a potential replacement of the conventional PCB finishes because of environment-friendly process, high corrosion-resistance and long shelf life over 1 year. In this study, solder joint properties of the plasma organic surface finish were estimated and compared with OSP surface finish. The plasma surface finish was deposited by chemical vapor deposition from fluorine-based precursors. The thickness of the plasma organic coating was 20 nm. Sn-3.0Ag-0.5Cu (SAC305) solder was used as solder joint materials. From a salt spray test, the plasma organic coating had higher corrosion resistance than the OSP surface finish. The spreadability of SAC305 on plasma organic coating was higher than that on OSP surface finish. SEM and TEM micrographs showed that the interfacial microstructure of the plasma surface finish sample were similar to that of the OSP sample. Solder joint strength of the plasma finish sample was also similar to that of the OSP finished sample.

Pyrolytic carbon: factors controlling in-rubber performance

Pyrolysis of waste tyres not only tackles the environmental issues associated with disposal, but also enables the recovery of valuable products such as oils and carbon fillers for elastomeric materials. This study was instigated to benchmark the in-rubber properties of pyrolytic carbon (often referred to as pyrolysis carbon black, pCB) and to understand the compositional parameters that dictate performance. Colloidal properties suggest the pCB materials to have a reinforcing potential between that of N330 and N550 carbon blacks, whereas physical property data suggest that they are more akin to the N700 series. Fundamentally, this disparity in performance appears to be the result of carbonaceous residues on the pCB surface, which both reduce surface activity and dispersability of the recyclate. Both thermogravimetric and dynamic mechanical analyses confirmed a number of pCB samples to have the same specific surface activity, regardless of the pyrolysis process or feedstock utilised.

세라믹을 이용한 적층형 유전체 도파관 필터

본 논문에서는 적층형 유전체 도파관 필터를 제안한다. 횡 방향으로 공진부가 연결되는 유전체 도파관 필터는 단수가 증가함에 따라 길이가 증가하여 제작시 어려움이 따른다. 제안된 구조는 세라믹을 이용하여 일부 공진부를 적층 형태로 변경하여 설계 제작한 것이다. 상대 유전율이 22인 세라믹을 이용하여 기존의 도파관 필터보다 25 % 정도 크기가 줄었으며, SMD 형태로 PCB에 표면 실장이 가능하도록 하였다. Layered-type dielectric waveguide filters were designed. As the order of layers increased the fabrication process for dielectric waveguide filters which the resonator parts were connected by the lateral direction has many difficulties. The proposed structure in this report was designed based on the layered-type for the some parts of resonators. The size of layered-type dielectric waveguide filters installed on the PCB surface were reduced at 25% as compared with the usual waveguide filters by using a relative dielectric constant 22.

Reliability Laboratory Analysis of PCB Surface Coating Based on ENEPIG

Electroless palladium are introduced to ENEPIG surface coating technology, from reaction principle to prevent oxidation of nickel-plated, but the process conditions and parameters of practical application are whether or not mass-produce condition , need using a series of reliability experiments to validate it , to reduce risk coefficient of mass-produce , to satisfy customer requirement. Therefore, put forward a package of experimental programs, including experiment projects, experiment methods, instrument and equipment for test, evaluate requirement, test result and analysis etc , especially using TEM have in-depth analysis for interface alloy compound of ENEPIG coating player with SAC305 , systematically verified ENEPIG production technology are mature and reliable, it is considered to be versatile surface coating technology, and particularly suitable for application in gold bonding and surface mount hybrid assembly board which are high connecting reliability product, completely replace the current ENIG technology.

Study of the effects of PCB surface finish on plasma process time for lead-free wave soldering

Purpose The purpose of this paper is to investigate the end point of the plasma cleaning process, in order to save valuable production time and also to prevent the destruction of expensive devices through overheating. Design/methodology/approach Post plasma cleaning analysis using dynamic contact angle (DCA) analysis and video microscope observations have been conducted on plasma treated Entec coated copper, hot air solder levelled (HASL) and electroless nickel immersion gold (ENIG) surfaces in order to determine the effect of surface finish on plasma process times. Post plasma cleaning and lead-free wave soldering analysis of the three surface finishes have been evaluated. Findings The DCA results indicate that the end-point for plasma cleaning of Entec coated copper is achieved within one to three minutes (indicated by a low contact angle hysteresis). Further cleaning after three minutes may lead to surface degradation and poor solder wettability. This is consistent with the results of the video microscope observations which show well soldered component leads and pads with good solder coverage for copper surface finish treated at a short plasma process time (one minute) and poorly soldered component leads and pads for a surface treated at a long process time (ten minutes). Similar work conducted on HASL and ENIG finishes show better results (well soldered component leads and solder pads) for longer plasma process times of five to ten minutes. Originality/value This paper indicates that plasma process time determines the wettability and solderability of the treated samples. It shows that the plasma conditions including the process time must be optimised and characterised for every application in order to avoid damage to expensive devices. The findings also give the confidence to implement plasma cleaning of lead-free (99.3Sn/0.7Cu) solder PCBs for fluxless soldering.

인쇄회로기판용 Au 패드의 산란 특성 측정 및 분석에 의한 산란 인자 추출

In this study, the influence of surface roughness on light scattering from Au pads on a PCB surface was investigated. Angular distributions of light scattered from Au pads with different surface roughness were measured for several incident angles. Diffusely-scattered light could be separated by using the fact that the amount of specularly-scattered light was directly related to surface roughness. The separated diffuse term was curve-fitted with a physics-based model, and then the related scattering parameters were extracted and compared with measured parameters.

The use of ionic liquids in metal finishing and printed circuit manufacture

This report is unusual, in that the subject matter has scarcely arrived in the industry. In fact, the 3 industrial contributions using ionic liquids (ILs) – electroplating of Cr from Cr(III), electropolishing of stainless steel, and pcb surface finishing with immersion Ag plating are still very much in the early pilot plant stages, with considerable input and help from the academic partners still needed. Most of the 55 delegates at the joint European Union funded IONMET/ PROSURF project meeting on 21 February at the Birmingham Medical Institute probably left with feelings varying between excitement at the possible future applications of ionic liquids metal finishing, and some caveats regarding potential technological pitfalls, and the place of ILs in the surface engineering marketplace.

Effects of multiple reflows on interfacial reaction and shear strength of SnAgCu and SnPb solder joints with different PCB surface finishes

Abstract The effects of multiple reflows (1, 2, 4, 6, 8, 10 numbers of reflow) on interfacial reaction and shear strength of Sn3.8Ag0.7Cu (SAC) and Sn37Pb (SP) joints were systematically investigated using electrolytic Ni/Au and organic solderability preservative (OSP) finished pad. In the case of OSP finished substrate, the well-known intermetallic compound (IMC) Cu6Sn5 was observed for both solders. While for the Ni/Au finished substrate, the IMC Ni3Sn4 and (CuNi)6Sn5 were formed on the interface of SP and SAC joints, respectively. With the increasing number of reflows, the thickness of IMCs on all reaction couples increased gradually and the IMC grain coarsened. The IMC growth kinetics showed that the interfacial IMC Cu6Sn5 was controlled by grain boundary diffusion and that the IMCs (Ni3Sn4 and (CuNi)6Sn5) near Ni layer had interactive diffusion control of grain boundary and volume diffusion. Moreover, IMC growth at Cu interface was faster than that at Ni interface, irrespective of the solder type. Shear test results showed that the shear force did not change much until eight numbers of reflow for each reaction couple. The ductile fracture indicated that the shear strength of solder joints could not be significantly influenced by the thickness and morphology of the interfacial IMC.

Performance characteristics of a MPCM slurry cooled unit designed for telecommunication equipment

Optimum control of the PCB surface temperature is very important in achieving high performance and operational reliability of telecommunication equipment with high power density and thermal density. In this study, the performance of a liquid cooling unit with MPCM slurries (called as “MPCM cooled unit”) was tested and analyzed. In addition, its performance was compared with that of an air cooled unit and a water cooled unit. The maximum surface temperature and the index of uniform temperature distribution (IUTD) were introduced to analyze cooling performance. The surface temperature in the unit rack of telecommunication equipment can be controlled properly by using an MPCM cooled unit instead of an air cooled unit. The maximum surface temperature and IUTD of the MPCM cooled unit at the inlet temperature of 19°C were lower than those at inlet temperatures of 25°C and 27°C due to the increases of heat capacity and heat transfer rate. The heat capacity of the MPCM cooled unit increased significantly with the increase of mass flow rate due to high specific heat of MPCM particles with latent heat transfer rate. The cooling performance of the MPCM cooled unit was superior to that of the water cooled unit.

Cooling performance of a hybrid refrigeration system designed for telecommunication equipment rooms

During the last several years, the power density and thermal density of telecommunication equipments have been increased. The optimum control of the PCB surface temperature is very important for obtaining high performance and operation reliability of telecommunication equipments. In this study, the cooling characteristics of telecommunication equipments were measured and analyzed as a function of the equipments’ heat density. In addition, the performance of a novel hybrid refrigeration system for telecommunication equipment rooms was measured at various operating conditions. The PCB surface temperature ranged from 35 to 60 °C, which was relatively higher than the air temperature due to heat trapping and improper air distribution. The hybrid refrigeration system operated in the vapor compression cooling mode at high outdoor temperatures, but in the secondary fluid cooling mode at low outdoor temperatures. The outdoor temperature for the mode switch was approximately 8.3 °C. The COP of the hybrid refrigeration system was significantly enhanced at low outdoor temperatures as compared with the conventional vapor compression system due to no operation of the compressor.

Mechanical and microstructural properties of SnAgCu solder joints

Mechanical and microstructural properties of SnAgCu solder joints with hypoeutectic, eutectic and hypereutectic compositions were studied. Eutectic SnPb joints were used as the reference. Reflowed lap shear specimens made of FR-4 glass epoxy printed circuit boards with OSP and NiAu surface finishes were used in the tests. Mechanical properties and microstructural features of the joints were examined in the as-reflowed condition and after isothermal aging at 85°C for 1000h. Both the composition and PCB surface finish had a notable effect on the mechanical behaviour of the SnAgCu solder joints. The shear strength value of SnAgCu solder joints was mainly dependent on the size and distribution of Ag3Sn dispersions. The coarseness of the dispersions depends strongly on the amount of Ag in the solder alloy, the cooling rate after the reflow and the aging history of the solder joints.

Environment-Friendly Electronics: Lead-Free Technology

Environment-Friendly Electronics: Lead-Free Technology

Effect of PCB surface finish on creep properties of lead‐free solder joints

Purpose – To provide further knowledge of the effect of solder composition and PCB surface finish on the creep properties of lead‐free SnAgCu solder joints.Design/methodology/approach – Single‐overlap shear specimens were prepared for the creep testing. The test matrix included three different SnAgCu pastes with hypoeutectic, eutectic, and hypereutectic compositions. An Sn63Pb37 solder paste was used as a reference. The PCB finishes used were NiAu, organic solderability preservative (OSP) and immersion tin. The creep tests were performed at 85 and 105°C using a dead‐weight system.Findings – According to the results, the SnAgCu solder with eutectic or near‐eutectic composition is the safest choice when the creep behaviour of solder joints is considered. Of the three different PCB surface finishes, immersion tin is the most favourable choice for use with SnAgCu joints when creep is the predominant deformation mechanism in the joints. On the NiAu finish the creep properties of SnAgCu solder joints were signi...

The effect of PCB surface finish on lead‐free solder joints

PurposeTo study the behaviour of voids in PBGA solder joints and their influence on the lifetime of lead‐free solder joints.Design/methodology/approachThe behaviour of voids was studied using micro via and land pad PWBs, PBGA components, and by measuring voids in the solder joints. The lifetimes of solder joints were tested using accelerated temperature tests.FindingsNumber of factors affecting the solder joint lifetimes were found. The voids were discovered to have a significantly large influence on the solder joints.Practical implicationsThe findings can be used to achieve better soldering results, methods, and designs.Originality/valueIn this paper, the effect and the behaviour of voids were studied profoundly. The findings can be valuable to researchers and process personnel.