Study of Print Release Process in Solder Paste Printing

1995 ◽  
Vol 117 (3) ◽  
pp. 230-234 ◽  
Author(s):  
C. Sahay ◽  
L. M. Head ◽  
R. Shereen ◽  
P. Dujari ◽  
J. H. Constable ◽  
...  
Keyword(s):  
Shear Strength ◽  
Print Quality ◽  
Solder Paste ◽  
Release Process ◽  
Wall Area ◽  
Soldering Process ◽  
Solder Paste Printing ◽  
Lift Off ◽  
Definition Of ◽  
Paste Properties

Solder paste printing is central to the mass reflow soldering process for surface mount technology. The miniaturization of components has put an increased demand on the printing process and requires it to successfully print 75 μm-100 μm(3 to 4 mil) wide apertures. The amount of solder paste deposited is a matter of concern. This study presents results from experiments on printing with apertures having circular, rectangular, square and triangular geometries. The ratio of the printed volume to the aperture volume has been used as a definition of print quality. It was observed that acceptable prints were obtained when the ratio of aperture area to the aperture wall area was more than 0.8. A simple analytical model is also presented for the release of solder paste as the stencil separates from the substrate board assuming that the apertures were filled. The solder is currently treated as a single phase material with Newtonian behavior. The motion of solder paste in the stencil aperture is modelled as the developing viscous flow with velocity boundary layers developing along the walls. The shear strength of the paste is used to determine the area sticking to the wall, thus making it possible to get an estimate of the print quality. The model incorporates the effect of paste properties like viscosity, density, tack and shear strength, and other process variables like aperture dimensions and separation (lift off) velocities between the stencil and the board in predicting the print quality. The model predicts the effect of shear to tack strength of the paste, stencil thickness, and the ratio of aperture to wall area ratio on print quality.

Determination of Shear Stress at a Solder Paste/Stencil Interface

1993 ◽  
Vol 323 ◽  
Author(s):  
Linda M. Head ◽  
Vincent Rogers ◽  
Chitteranjan Sahay ◽  
James Constable
Keyword(s):  
Shear Stress ◽  
Mechanical Test ◽  
Test Procedure ◽  
Shear Thinning ◽  
Solder Paste ◽  
Parallel Plates ◽  
Release Process ◽  
Stencil Printing ◽  
Plate Separation ◽  
Lift Off

AbstractTo create a model for the release process of solder paste during stencil printing for surface mount applications it is necessary to determine the shear stress developed at the interface between the solder paste and stencil sidewall. An experiment has been developed to determine the value of the shear stress for solder paste samples. For the purpose of this experiment a Micro-mechanical tester has been adapted and programmed to provide both a shear thinning cycle and a pull-off cycle that simulate aperture fill and stencil lift-off. The shear stress developed at the solder/stencil-sidewall interface is estimated from the data obtained during the pull-off portion of the Micro-mechanical test procedure. The micro-mechanical tester is fitted with a set of parallel plates that can be adjusted for plate separation and surface roughness.The experiment consists of two parts: (1) the shear thinning cycle and (2) the horizontal pull-off. After application of the solder paste and adjustment of plate separation, a back and forth movement of the upper plate provides shear thinning of the paste. This step is necessary to simulate the shear thinning that occurs from the application of squeege pressure during aperture fill. The horizontal pull-off then simulates the lift-off step of the stencil printing procedure. During the horizontal pull-off data is. taken which allows calculation of the force developed as the upper plate is pulled away from the lower. Results from this experiment show the values of shear stress that develop during pull-off with a variation of surface treatments and plate separations.This paper will present the experimental set-up, a description of the relationship between this experiment and the actual stencil lift-off process, and shear stress data that has been acquired for a variety of solder pastes and plate separations.

Analysis of Solder Paste Release in Fine Pitch Stencil Printing Processes

1999 ◽  
Vol 121 (3) ◽  
pp. 169-178 ◽  
Author(s):  
G. Rodriguez ◽  
D. F. Baldwin
Keyword(s):  
High Speed ◽  
Flip Chip ◽  
Imaging System ◽  
Main Process ◽  
Print Quality ◽  
Solder Paste ◽  
Release Process ◽  
Stencil Printing ◽  
Fine Pitch ◽  
Analytical Approaches

Advanced electronics packaging technologies such as chip scale packages, fine pitch ball grid arrays, and flip chip are pushing solder paste stencil printing to the limit. In order to achieve solder print deposits of the sizes required for emerging electronic packaging technology, a rigorous understanding of the process is required. This paper seeks to expand our understanding of the physical characteristics of stencil printing specifically focusing on the solder paste release process based on experimental and analytical approaches. First, designed experiments were conducted to identify the main process variables affecting final print quality. An in-situ measurement system using a high speed imaging system monitored the solder paste release process. Based on experimental observations, different modes of solder paste release and their corresponding mechanisms were identified. A model was developed to predict print quality for fine pitch applications. The proposed model was experimentally verified showing good agreement with measured values for fine pitch and very fine pitch printing. It was found that the cohesive and adhesive forces acting on the paste tend to govern the release process rather than the viscous and inertial forces.

Modeling the Thermal Behavior of Solder Paste Inside Reflow Ovens

2003 ◽  
Vol 125 (3) ◽  
pp. 335-346 ◽  
Author(s):  
A. Tava´rez ◽  
J. E. Gonza´lez
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Solder Paste ◽  
Soldering Process ◽  
Coupled Heat Transfer ◽  
Numerical Predictions ◽  
Loss Of Weight ◽  
Manufacturing Applications ◽  
Free Solder ◽  
Paste Properties

The development of a mathematical model of the soldering process of actual pastes as used in surface mount technology (SMT) lines is described in this paper. The coupled heat transfer processes between the solder paste and the flux including changes in solder paste properties are considered in the model. Specifically, the loss of solvents in the vehicle system, melting, solidification and further single phase cooling of the solder paste are contemplated in the model. Experiments were conducted with the objective of validating the predictions of the solder paste temperature profile and of the loss of weight due to flux extraction. Results are shown in this paper for typical eutectic paste 63%Sn-37%Pb and experimental data is in good agreement with the numerical predictions. Simulations using the lead-free solder paste systems 96.5%Sn-3.5%Ag and 42%Sn-58%Bi are also reported in this paper. The proposed model is suitable for incorporation into existing three dimensional heat transfer models of PCBs for simulations in ovens with similar characteristics as those used in actual manufacturing applications.

Analysis of the Micro-Mechanical Properties in Aged Lead-Free, Fine Pitch Flip Chip Joints

2003 ◽  
Author(s):  
Changqing Liu ◽  
Paul Conway ◽  
Dezhi Li ◽  
Michael Hendriksen
Keyword(s):  
Shear Strength ◽  
Flip Chip ◽  
Printed Circuit Board ◽  
Initial Period ◽  
Electroless Nickel ◽  
Circuit Board ◽  
Solder Paste ◽  
Soldering Process ◽  
Joint Reliability ◽  
Solder Bumps

This research seeks to characterize the micro-mechanical behavior of Sn-Ag-Cu solder bumps/joints generated by fine feature flip chip fabrication and assembly processes. The bumps used for characterization were produced by stencil deposition of solder paste onto an electroless Nickel UBM, followed by a bump-forming reflow soldering process and the final assembly joints were then achieved by a subsequent reflow of die onto a fine feature Printed Circuit Board (PCB). The bumps and joints were aged at either 80°C or 150°C for up to 1.5 months and then analyzed by means of micro-shear testing and nano-indentation techniques. The shear test of the aged bumps showed a slight increase in shear strength after an initial period of aging (∼ 50h) as compared to as-manufactured bumps, but a decrease after longer aging (e.g. 440 h). A brittle Ag3Sn phase formed as large lamellae in the solder and along the interface between the Cu on the PCB during the initial aging, and is attributed to the increase of shear strength, along with the refinement of the bump microstructure. However, as the time of aging extended, the solder bumps were softened due to grain growth and re-crystallization. It was found that the formation of brittle phases in the solder and along the interfaces caused localized stress concentration, which can significantly affect joint reliability. In addition, Nano-testing identified a lamellar Au-rich structure, formed in the solder and interface of the solder/PCB in the joints after the aging process. These are believed to be detrimental to joint reliability.

Determination of In-plane Shear Strength of Unidirectional Composite Materials Using the Off-axis Three-point Flexure and Off-axis Tensile Tests

2010 ◽  
Vol 44 (21) ◽  
pp. 2487-2507 ◽  
Author(s):  
G. Vargas ◽  
F. Mujika
Keyword(s):  
Shear Strength ◽  
Composite Materials ◽  
Tensile Tests ◽  
Unidirectional Composite ◽  
Point Of View ◽  
Experimental Point ◽  
Plane Shear ◽  
Lift Off ◽  
Flexure Test

The aim of this work is to compare from an experimental point of view the determination of in-plane shear strength of unidirectional composite materials by means of two off-axis tests: three-point flexure and tensile. In the case of the off-axis three-point flexure test, the condition of small displacements and the condition of lift-off between the specimen and the fixture supports have been taken into account. Some considerations regarding stress and displacement fields are presented. The in-plane shear characterization has been performed on a carbon fiber reinforced unidirectional laminate with several fiber orientation angles: 10°, 20°, 30°, and 45°. Test conditions for both off-axis experimental methods, in order to ensure their applicability, are presented. Off-axis flexure test is considered more suitable than off-axis tensile test for the determination of in-plane shear strength.

Surface acoustic wave resonator from thick MOVPE-grown layers of GaN(0001) on sapphire

2002 ◽  
Vol 743 ◽  
Author(s):  
Sverre V. Pettersen ◽  
Thomas Tybell ◽  
Arne Rønnekleiv ◽  
Stig Rooth ◽  
Veit Schwegler ◽  
...  
Keyword(s):  
Acoustic Wave ◽  
Surface Acoustic Wave ◽  
Electromechanical Coupling ◽  
Film Surface ◽  
Center Frequency ◽  
Electromechanical Coupling Coefficient ◽  
Nitride Film ◽  
Wave Resonator ◽  
Lift Off ◽  
Definition Of

ABSTRACTWe report on fabrication and measurement of a surface acoustic wave resonator prepared on ∼10m thick GaN(0001) films. The films were grown by metal-organic vapor phase epitaxy on a c-plane sapphire substrate. The surface morphology of the films were examined with scanning electron and atomic force microscopy. A metallic bilayer of Al/Ti was subsequently evaporated on the nitride film surface. Definition of the resonator interdigital transducers, designed for a wavelength of λ=7.76m, was accomplished with standard UV lithography and lift-off. S-parameter measurements showed a resonator center frequency f0=495MHz at room temperature, corresponding to a surface acoustic wave velocity of 3844m/s. The insertion loss at center frequency was measured at 8.2dB, and the loaded Q-factor was estimated at 2200. Finally, measurements of the resonator center frequency for temperatures in the range 25–155°C showed a temperature coefficient of -18ppm/°C. The intrinsic GaN SAW velocity and electromechanical coupling coefficient were estimated at νSAW=383 1m/s and K2=1.8±0.4·10−3.

Impact of non-uniform water absorption on water-interference print mottle in offset printing

2018 ◽  
Vol 33 (1) ◽  
pp. 150-163 ◽  
Author(s):  
Sofia Thorman ◽  
Göran Ström ◽  
Patrick A. C. Gane
Keyword(s):  
Moisture Absorption ◽  
Staining Technique ◽  
Relevant Information ◽  
Print Quality ◽  
Surface Adhesion ◽  
Offset Printing ◽  
Surface Moisture ◽  
Coated Papers ◽  
Burn Out ◽  
Lift Off

Abstract Print mottle is a serious and yet common print defect in offset printing. An imbalance between the feed of fountain solution and the ability of the paper substrate to absorb and transport this water away from the surface can cause moisture/water interference problems. In the study presented here, we have investigated the uniformity of aqueous absorption and coating structure of pilot-coated papers with different types and dosages of dispersants and linked this to print mottle and uncovered areas (UCA). In earlier studies, the print quality of these papers indicated that a moderate addition of excess dispersant caused ink refusal, ink-lift-off (ink-surface adhesion failure) and water-interference mottle when printing at elevated fountain feed. In the present study, we have shown that a majority of the samples with uneven water/moisture absorption and an uneven burn-out reflectance tended to have more severe printing problems related to surface-moisture/water.An aqueous staining technique was used to characterise the absorption non-uniformities. This method has been developed previously with focus on absorption of flexographic water-based inks but can clearly give relevant information also for offset printing, when it comes to moisture/water interference mottle.

scholarly journals Head-on-Pillow Defect Detection: X-Ray Inspection Limitations

2019 ◽  
Vol 16 (2) ◽  
pp. 91-102
Author(s):  
Lars Bruno ◽  
Benny Gustafson
Keyword(s):  
Solder Joints ◽  
Solder Paste ◽  
Wafer Level ◽  
Reflow Soldering ◽  
X Ray ◽  
Soldering Process ◽  
Irregular Shapes ◽  
Fine Pitch ◽  
Solder Balls ◽  
Ball Grid Array Packages

Abstract Both the number and the variants of ball grid array packages (BGAs) are tending to increase on network printed board assemblies with sizes ranging from a few millimeter die size wafer level packages with low ball count to large multidie system-in-package (SiP) BGAs with 60–70 mm side lengths and thousands of I/Os. One big challenge, especially for large BGAs, SiPs, and for thin fine-pitch BGA assemblies, is the dynamic warpage during the reflow soldering process. This warpage could lead to solder balls losing contact with the solder paste and its flux during parts of the soldering process, and this may result in solder joints with irregular shapes, indicating poor or no coalescence between the added solder and the BGA balls. This defect is called head-on-pillow (HoP) and is a failure type that is difficult to determine. In this study, x-ray inspection was used as a first step to find deliberately induced HoP defects, followed by prying off of the BGAs to verify real HoP defects and the fault detection correlation between the two methods. The result clearly shows that many of the solder joints classified as potential HoP defects in the x-ray analysis have no evidence at all of HoP after pry-off. This illustrates the difficulty of determining where to draw the line between pass and fail for HoP defects when using x-ray inspection.

Ultra-Thin, Fine-Pitch Step Stencils For Miniature Component Assembly

2017 ◽  
Vol 2017 (DPC) ◽  
pp. 1-18
Author(s):  
Phani Vallabhajosyula
Keyword(s):  
Visual Inspection ◽  
Flip Chip ◽  
Print Quality ◽  
Solder Paste ◽  
3D Measurement ◽  
Aperture Size ◽  
Fine Pitch ◽  
Technology Applications ◽  
Component Assembly ◽  
Special Step

Mixed technology applications for Flip-Chip (FC) / SMT require special step stencil designs where flux is printed first for the FC and SMD paste printed next with a second stencil that has a relief pocket etched or formed in the FC area. Step stencils are used when varying stencil thicknesses are required to print into cavities or on elevated surfaces or to provide relief for certain features on a board. In the early days of SMT assembly, Step Stencils were used to reduce the stencil thickness for 25 mil pitch leaded device apertures. Thick metal stencils that have both relief-etch pockets and reservoir step pockets are very useful for paste reservoir printing. However as SMT requirements became more complex and consequently more demanding so did the requirements for complex Step Stencils. Electroform Step-Up Stencils for ceramic BGA's and RF Shields are a good solution to achieve additional solder paste height on the pads of these components as well as providing exceptional paste transfer for smaller components like uBGAs and 0201s. As the components are getting smaller, for example 0201m, or as the available real estate for component placement on a board is getting smaller – finer is the aperture size and pitch on the stencils. Aggressive distances from step wall to aperture are also required. Ultra-thin stencils with thicknesses in the order of 40um with steps of 13um are used to obtain desired print volume. These applications and the associated stencil design to achieve a solution will be discussed in detail in this paper. Various print experiments will be conducted and print quality will be determined by visual inspection and 3D measurement of the paste deposit to understand the volume transfer efficiency.

Effect of aluminium substrate thickness on the lap-shear strength of adhesively bonded and hybrid riveted-bonded joints

2020 ◽  
pp. 095440892091343
Author(s):  
VC Beber ◽  
N Wolter ◽  
B Schneider ◽  
K Koschek
Keyword(s):  
Shear Strength ◽  
Failure Process ◽  
Lap Joints ◽  
Substrate Thickness ◽  
Bonded Joints ◽  
Adhesively Bonded ◽  
Lap Shear Strength ◽  
Lap Shear ◽  
Definition Of ◽  
Structural Adhesive

For lightweight materials, e.g. aluminium, the definition of proper joining technology relies on material properties, as well as design and manufacturing aspects. Substrate thickness is especially relevant due to its impact on the weight of components. The present work compares the performance of adhesively bonded (AJ) to hybrid riveted-bonded joints (HJ) using aluminium substrates. To assess the lightweight potential of these joining methods, the effect of substrate thickness (2 and 3 mm) on the lap-shear strength (LSS) of single lap joints is investigated. An epoxy-based structural adhesive is employed for bonding, whilst HJs are produced by lockbolt rivet insertion into fully cured adhesive joints. The stiffness of joints increased with an increase of substrate thickness. HJs presented two-staged failure process with an increase in energy absorption and displacement at break. For HJs, the substrate thickness changed the failure mechanism of rivets: with thicker substrates failure occurred due to shear, whereas in thinner substrates due to rivet pulling-through. The LSS of 2 mm and 3 mm-thick AJs is similar. With 2 mm-thick substrates, the LSS of HJs was lower than AJs. In contrast, the highest LSS is obtained by the 3 mm-thick HJs. The highest lightweight potential, i.e. LSS divided by weight, is achieved by the 2 mm-thick AJs, followed by the 3 mm-thick HJs with a loss of ca. 10% of specific LSS.

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