Technical Library | 2007-08-16 13:34:31.0
While experienced inspectors may be able to determine the aesthetic differences between a lead-free PCB assembly and a tin-lead version, one cannot rely on the "experienced eye". "Less wetting out to the pad edges" (Figure A) and "graininess and lack of shininess of the solder joint" (Figure B) are typical comments about some lead-free solder joints. However, in cases where a Nitrogen atmosphere was present during the reflow of the solder joint (Figure C), there will be little visual differences between the lead free alloys and their tin-lead counterparts.
Technical Library | 2016-05-26 15:07:36.0
The oxide layers are known as wetting inhibitors in component and PCB metallizations. The oxide acts as barrier that prevent the tin diffusion from happening. Besides, in corrosion studies, the role of salt residues -with Cl ion- on some metals is known as being promoters of oxidation or corrosion. On the other hand, most of corrosion studies with tin metallization are focused mainly on the corrosion resistance of tin alloys, but little has been done respecting to the influence of salts on tin metallization wetting. In this paper, a series of experiments was carried over to know the influence of specifically NaCl on BGA wetting given Head in Pillow (HiP) as result.
Technical Library | 2021-07-06 21:13:36.0
The surface finishes commonly used on printed circuit boards (PCBs) have an effect on solder paste performance in the surface mount process. Some surface finishes are non-planar like hot air solder level (HASL) which can lead to inconsistencies in solder paste printing. Other surface finishes are difficult to wet during reflow like organic solderability preservative (OSP). What is the overall effect of surface finish on solder paste performance? Which solder paste is best for each surface finish? It is the goal of this paper to answer these questions.
Technical Library | 2021-10-20 18:21:06.0
The solderability of the SAC305 alloy in contact with printed circuit boards (PCB) having different surface finishes was examined using the wetting balance method. The study was performed at a temperature of 260 _C on three types of PCBs covered with (1) hot air solder leveling (HASL LF), (2) electroless nickel immersion gold (ENIG), and (3) organic surface protectant (OSP), organic finish, all on Cu substrates and two types of fluxes (EF2202 and RF800). The results showed that the PCB substrate surface finish has a strong effect on the value of both the wetting time t0 and the contact angle h. The shortest wetting time was noted for the OSP finish (t0 = 0.6 s with EF2202 flux and t0 = 0.98 s with RF800 flux), while the ENIG finish showed the longest wetting time (t0 = 1.36 s with EF2202 flux and t0 = 1.55 s with RF800 flux). The h values calculated from the wetting balance tests were as follows: the lowest h of 45_ was formed on HASL LF (EF2202 flux), the highest h of 63_ was noted on the OSP finish, while on the ENIG finish, it was 58_ (EF2202 flux). After the solderability tests, the interface characterization of cross-sectional samples was performed by means of scanning electron microscopy coupled with energy dispersive spectroscopy.
Technical Library | 2014-01-30 18:08:04.0
As of today, the electronic industry is aware of the requirements for their products to be lead free. All components are typically available in lead free quality. This comprises packages like BGAs with BGA solder balls to PCB board finishes like HASL. The suppliers are providing everything that is needed. It is harder to get the old tin leaded (SnPb) components for new applications today, than lead free ones. So why has not everybody changed over fully yet and how can the challenges be overcome? A big concern in this transition process is reflow soldering. The process temperatures for lead free applications became much higher. Related with this is more stress for all the components. It affects the quality and reliability of the electronic units and products...
Technical Library | 2013-01-24 19:16:35.0
The electronics industry has mainly adopted the higher melting point Sn3Ag0.5Cu solder alloys for lead-free reflow soldering applications. For applications where temperature sensitive components and boards are used this has created a need to develop low melting point lead-free alloy solder pastes. Tin-bismuth and tin-bismuth-silver containing alloys were used to address the temperature issue with development done on Sn58Bi, Sn57.6Bi0.4Ag, Sn57Bi1Ag lead-free solder alloy pastes. Investigations included paste printing studies, reflow and wetting analysis on different substrates and board surface finishes and head-in-pillow paste performance in addition to paste-in-hole reflow tests. Voiding was also investigated on tin-bismuth and tin-bismuth-silver versus Sn3Ag0.5Cu soldered QFN/MLF/BTC components. Mechanical bond strength testing was also done comparing Sn58Bi, Sn37Pb and Sn3Ag0.5Cu soldered components. The results of the work are reported.
Technical Library | 2023-08-04 15:27:30.0
A designed experiment evaluated the influence of several variables on appearance and strength of Pb-free solder joints. Components, with leads finished with nickel-palladium-gold (NiPdAu), were used from Texas Instruments (TI) and two other integrated circuit suppliers. Pb-free solder paste used was tin-silver-copper (SnAgCu) alloy. Variables were printed wiring board (PWB) pad size/stencil aperture (the pad finish was consistent; electrolysis Ni/immersion Au), reflow atmosphere, reflow temperature, Pd thickness in the NiPdAu finish, and thermal aging. Height of solder wetting to component lead sides was measured for both ceramic plate and PWB soldering. A third response was solder joint strength; a "lead pull" test determined the maximum force needed to pull the component lead from the PWB. This paper presents a statistical analysis of the designed experiment. Reflow atmosphere and pad size/stencil aperture have the greatest contribution to the height of lead side wetting. Reflow temperature, palladium thickness, and preconditioning had very little impact on side-wetting height. For lead pull, variance in the data was relatively small and the factors tested had little impact.
Technical Library | 2014-03-06 19:04:07.0
Over the last few years, there has been an increase in the rate of Head-in-Pillow component soldering defects which interrupts the merger of the BGA/CSP component solder spheres with the molten solder paste during reflow. The issue has occurred across a broad segment of industries including consumer, telecom and military. There are many reasons for this issue such as warpage issues of the component or board, ball co-planarity issues for BGA/CSP components and non-wetting of the component based on contamination or excessive oxidation of the component coating. The issue has been found to occur not only on lead-free soldered assemblies where the increased soldering temperatures may give rise to increase component/board warpage but also on tin-lead soldered assemblies.
Technical Library | 2013-01-17 15:37:21.0
A problem exists with electroless nickel / immersion gold (ENIG) surface finish on some pads, on some boards, that causes the solder joint to separate from the nickel surface, causing an open. The solder has wet and dissolved the gold. A weak tin to nickel intermetallic bond initially occurs, but the intermetallic bond cracks and separates when put under stress. Since the electroless nickel / immersion gold finish performs satisfactory in most applications, there had to be some area within the current chemistry process window that was satisfactory. The problem has been described as a 'BGA Black Pad Problem' or by HP as an 'Interfacial Fracture of BGA Packages…'[1]. A 24 variable experiment using three different chemistries was conducted during the ITRI (Interconnect Technology Research Institute) ENIG Project, Round 1, to investigate what process parameters of the chemical matrix were potentially satisfactory to use and which process parameters of the chemical matrix need to be avoided. The ITRI ENIG Project has completed Round 1 of testing and is now in the process of Round 2 TV (Test Vehicle) build.
Technical Library | 2019-05-01 23:18:27.0
Moisture can accelerate various failure mechanisms in printed circuit board assemblies. Moisture can be initially present in the epoxy glass prepreg, absorbed during the wet processes in printed circuit board manufacturing, or diffuse into the printed circuit board during storage. Moisture can reside in the resin, resin/glass interfaces, and micro-cracks or voids due to defects. Higher reflow temperatures associated with lead-free processing increase the vapor pressure, which can lead to higher amounts of moisture uptake compared to eutectic tin-lead reflow processes. In addition to cohesive or adhesive failures within the printed circuit board that lead to cracking and delamination, moisture can also lead to the creation of low impedance paths due to metal migration, interfacial degradation resulting in conductive filament formation, and changes in dimensional stability. Studies have shown that moisture can also reduce the glass-transition temperature and increase the dielectric constant, leading to a reduction in circuit switching speeds and an increase in propagation delay times. This paper provides an overview of printed circuit board fabrication, followed by a brief discussion of moisture diffusion processes, governing models, and dependent variables. We then present guidelines for printed circuit board handling and storage during various stages of production and fabrication so as to mitigate moisture-induced failures.
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