The Benefits of Flux-Coated Solder Preforms in a QFN Assembly Process

2015 ◽  
Vol 2015 (1) ◽  
pp. 000827-000832
Author(s):  
Brandon Judd ◽  
Maria Durham
Keyword(s):  
Mechanical Properties ◽  
Form Factor ◽  
Solder Joint ◽  
Circuit Board ◽  
Electrical Performance ◽  
Solder Paste ◽  
Assembly Process ◽  
Circuit Board Assembly ◽  
Difficult Challenge ◽  
Small Form Factor

The use of bottom terminated components (BTCs) such as quad-flat no-leads (QFNs) has become commonplace in the circuit board assembly world. This package offers several benefits including its small form factor, its excellent thermal and electrical performance, easy PCB trace routing, and reduced lead inductance. These components are generally attached to PWBs PCBs via solder paste. The design of these components with the large thermal pad, along with the tendency of solder paste to outgas during reflow from the volatiles in the flux, creates a difficult challenge in terms of voiding control within the solder joint. Voiding can have a serious effect on the performance of these components, including the mechanical properties of the joint as well as spot overheating. Solder preforms with a flux coating can be added to the solder paste to help reduce voiding. This study will focus on the benefits of utilizing solder preforms with modern flux coatings in conjunction with solder paste to help reduce voiding under QFNs, as well as the design and process parameters which provide optimal results.

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

2016 ◽  
Vol 2016 (1) ◽  
pp. 000711-000720
Author(s):  
Brandon Judd ◽  
Maria Durham
Keyword(s):  
Hot Spots ◽  
Mesh Size ◽  
Daily Basis ◽  
Circuit Board ◽  
Electrical Performance ◽  
Solder Paste ◽  
Process Variables ◽  
Circuit Board Assembly ◽  
Material Process ◽  
Small Form Factor

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.

scholarly journals An intelligent approach for improving printed circuit board assembly process performance in smart manufacturing

2020 ◽  
Vol 12 ◽  
pp. 184797902094618
Author(s):  
Vincent WC Fung ◽  
Kam Chuen Yung
Keyword(s):  
Printed Circuit Board ◽  
Circuit Board ◽  
Smart Manufacturing ◽  
Process Performance ◽  
Solder Paste ◽  
Assembly Process ◽  
Printed Circuit Board Assembly ◽  
Printed Circuit ◽  
Circuit Board Assembly ◽  
Solder Paste Printing

The process of printed circuit board assembly (PCBA) involves several machines, such as a stencil printer, placement machine and reflow oven, to solder and assemble electronic components onto printed circuit boards (PCBs). In the production flow, some failure prevention mechanisms are deployed to ensure the designated quality of PCBA, including solder paste inspection (SPI), automated optical inspection (AOI) and in-circuit testing (ICT). However, such methods to locate the failures are reactive in nature, which may create waste and require additional effort to be spent re-manufacturing and inspecting the PCBs. Worse still, the process performance of the assembly process cannot be guaranteed at a high level. Therefore, there is a need to improve the performance of the PCBA process. To address the aforementioned challenges in the PCBA process, an intelligent assembly process improvement system (IAPIS) is proposed, which integrates the k-means clustering method and multi-response Taguchi method to formulate a pro-active approach to investigate and manage the process performance. The critical process parameters are first identified by means of k-means clustering and the selected parameters are then used to formulate a set of experimental studies by using the multi-response Taguchi method to optimize the performance of the assembly process. To validate the proposed system, a case study of an electronics manufacturer in the solder paste printing process was conducted. The contributions of this study are two-fold: (i) pressure, blade angle and speed are identified as the critical factors in the solder paste printing process; and (ii) a significant improvement in the yield performance of PCBA can be achieved as a component in the smart manufacturing.

The Effect of Nano-Cu Particles on Mechanical Properties of Micro-Joining Joint with Lead-Free Solder

2011 ◽  
Vol 291-294 ◽  
pp. 929-933
Author(s):  
Ying Ming Shen ◽  
Fang Juan Qi ◽  
Min Xie ◽  
Jian Li
Keyword(s):  
Mechanical Properties ◽  
Solder Joint ◽  
Lead Free ◽  
Fatigue Properties ◽  
Lead Free Solder ◽  
Solder Paste ◽  
Shearing Strength ◽  
Free Solder

The effect of nano-Cu particles on mechanical bend reliability of micro-joining joint with Sn-3.5Ag lead free solder was studied in this paper. The results show that 0.5% nano-Cu composite lead free solder show significantly better shearing strength and mechanical bend fatigue properties than eutectic Sn-3.5Ag solder paste, 1.0% nano-Cu composites and 1.5% nano-Cu composites. The further analysis shows that adding nano-Cu particles make much effect on intermetallic (IMC) in the interface of micro-joint and the inside of the solder joint. The different interface of micro-joining joint induced different mechanical properties.

Pb-Free Thin Small Outline Package (TSOP) Board Level Reliability Study

2009 ◽  
Author(s):  
Weidong Xie ◽  
Kuo-Chuan Liu ◽  
Mark Brillhart
Keyword(s):  
Solder Joint ◽  
Coefficient Of Thermal Expansion ◽  
Circuit Board ◽  
Solder Paste ◽  
Eutectic Solder ◽  
Qualification Testing ◽  
Free Solder ◽  
Board Level ◽  
The Impact

Thin Small Outline Package (TSOP) are one of the most commonly used surface mount components due to its low overall cost. Traditionally leadframe packages such as TSOP or Quad Flat Package (QFP) are less of a concern (if assembled with SnPb eutectic solder paste) about their long term reliability and often exempted from board level qualification testing as the mechanical compliance of metal leads mitigate the stresses due to the Coefficient of Thermal Expansion (CTE) mismatch between the package and Print Circuit Board (PCB). Therefore more attention has been put on the solder joint reliability of Pb-free Ball Grid Array (BGA) packages over leadframe packages while the industry is moving away from SnPb eutectic solder materials to meet RoHS regulatory requirements. The authors have observed that TSOPs if assembled with Pb-free solder materials could fail at very early stages during qualification testing (in some case as early as 300 cycles under standard 0°C to 100°C thermal cycling). Since most Pb-free solder materials such as SnAgCu are mechanically more rigid than SnPb eutectic solder material, higher stresses are expected be induced in solder joints during temperature excursions. Pb-free solder materials’ wicking behavior may also contribute to the early failures. In this study, long term reliability of a flash memory TSOP has been investigated. These tested TSOPs, assembled on 93mil-thick PCBs with SAC305 paste, are of two configurations: one with single die and the other with stacked quadruple dies. Some test vehicles have been thermally aged under four different thermal aging conditions to study the aging effect on Pb-free solder joint life. Finite element analysis (FEA) modeling has also been employed to further investigate the impact of other parameters such as die size, package size, and the number of dies that being stacked inside one package.

Developments in Stencil Printing Technology for 0.3mm Pitch CSP Assembly

2011 ◽  
Vol 2011 (1) ◽  
pp. 000502-000508 ◽  
Author(s):  
Mark Whitmore ◽  
Clive Ashmore
Keyword(s):  
Form Factor ◽  
Area Ratio ◽  
Transfer Efficiency ◽  
Solder Paste ◽  
Assembly Process ◽  
Next Generation ◽  
Stencil Printing ◽  
Printing Process ◽  
Fine Pitch ◽  
Solder Pastes

As electronics assemblies continue to shrink in form factor, forcing designers towards smaller components with decreasing pitches, the Surface Mount assembly process is becoming increasingly challenged. A new “active” squeegee printing process has been developed to assist in the stencil printing of solder pastes for next generation ultra fine pitch components such as 0.3mm pitch CSP’s. Results indicate that today’s accepted stencil area ratio rules, which govern solder paste transfer efficiency can be significantly pushed to extend stencil printing process capabilities to stencil apertures having area ratios as low as 0.4. Such a breakthrough will allow the printing of ultra fine pitch components and additionally will assist with heterogeneous assembly concerns, to satisfy up and coming mixed technology demands.

Displacement Theory for Fixturing Design of Thin Flexible Circuit Board Assembly

2000 ◽  
Vol 123 (4) ◽  
pp. 388-393
Author(s):  
Ruijun Chen ◽  
Daniel F. Baldwin
Keyword(s):  
Theoretical Foundation ◽  
Circuit Board ◽  
Flexible Substrates ◽  
Transverse Displacement ◽  
Assembly Process ◽  
Circuit Board Assembly ◽  
Displacement Theory ◽  
Bond Pads ◽  
The Impact ◽  
Displacement Model

The compliant nature of flexible substrates subject to assembly forces can result in severe misregistration of the component leads and substrate bond pads, leading to assembly process defects. Specially dedicated tooling for fixturing thin flexible substrates in standard surface mount assembly equipment is gaining importance. This paper focuses on developing a theoretical foundation for implementing Smart Tooling of fixturing thin flexible substrates. The primary goals are to determine the impact of fixturing tooling on assembly process quality, to develop a displacement theory to predict transverse displacements, and to analyze the optimum perimeter fixturing configuration. The predictive capabilities of the transverse displacement model are verified.

The Network Locating Principle in Flexible Circuit Board Assembly

2009 ◽  
Author(s):  
Ruijun Chen
Keyword(s):  
Flip Chip ◽  
Experimental Studies ◽  
Deformation Energy ◽  
Thermodynamic System ◽  
Circuit Board ◽  
Energy Change ◽  
Solder Paste ◽  
Circuit Board Assembly ◽  
Tooling Design ◽  
Thermoelastic Theory

This paper focuses on developing the Network Locating Principle for fixturing tooling design in flexible circuit board assembly. From a viewpoint of Thermodynamics, a flexible circuit board populated with electronic components on the first side is a closed thermodynamic system. It experiences deformation energy change, assembly load work, and heat transfer during an isothermal assembly process on the second side, such as solder paste deposit printing and electronic component placement processes. Based on the First and Second Laws of Thermodynamics and Energy Equation of Thermoelastic Theory, a fixturing analysis is developed to investigate the deformation energy change, and furthermore the theoretical fixturing solution is derived to minimize the assembly load work during the isothermal assembly processes. To this end, the Network Locating Principle is proposed to guide fixturing tooling design for the isothermal assembly processes on the second side. Effectiveness of the Network Locating Principle is verified in numerical and experimental studies of flip chip placement processes on a thin flexible circuit.

scholarly journals The Effect of Epoxy Polymer Addition in Sn-Ag-Cu and Sn-Bi Solder Joints

Materials ◽  
2019 ◽  
Vol 12 (6) ◽  
pp. 960 ◽  
Author(s):  
Min-Soo Kang ◽  
Do-Seok Kim ◽  
Young-Eui Shin
Keyword(s):  
Solder Joint ◽  
Strain Energy ◽  
Printed Circuit Board ◽  
Solder Joints ◽  
Circuit Board ◽  
Solder Paste ◽  
Element Analysis ◽  
Printed Circuit ◽  
Shock Testing ◽  
Polymer Addition

To analyze the reinforcement effect of adding polymer to solder paste, epoxies were mixed with two currently available Sn-3.0Ag-0.5Cu (wt.% SAC305) and Sn-59Bi (wt.%) solder pastes and specimens prepared by bonding chip resistors to a printed circuit board. The effect of repetitive thermal stress on the solder joints was then analyzed experimentally using thermal shock testing (−40 °C to 125 °C) over 2000 cycles. The viscoplastic stress–strain curves generated in the solder were simulated using finite element analysis, and the hysteresis loop was calculated. The growth and propagation of cracks in the solder were also predicted using strain energy formulas. It was confirmed that the epoxy paste dispersed the stress inside the solder joint by externally supporting the solder fillet, and crack formation was suppressed, improving the lifetime of the solder joint.

CONTROLLING AND OPTIMIZATION OF THERMAL PROFILE IN REFLOW SOLDERING

2009 ◽  
Vol 23 (06n07) ◽  
pp. 1949-1955
Author(s):  
JIANWEI SHI ◽  
PENG HE ◽  
XIAOCHUN LV
Keyword(s):  
Solder Joint ◽  
Circuit Board ◽  
Solder Paste ◽  
Thermal Profile ◽  
Reflow Soldering ◽  
Soldering Process ◽  
Joint Reliability ◽  
Controlling Parameter ◽  
Technical Evaluation ◽  
Reliability Of Solder Joints

Heating factor, Q is a quantitative parameter describing a process of reflow soldering. It can be used to evaluate a reflow soldering process and the reliability of solder joints. The value of Q is directly related to the energy absorbed by solder joint during heating and the morphology of Intermetallic Compound formed at the interface between solder and pad. Electronic product manufacturers use heating factor as a technical evaluation parameter to guide the adjustment of reflow soldering process and the optimization of reflow soldering curve, to ensure the best reliability of the circuit board. Solder paste manufacturers use heating factor to represent characteristics of their reflow soldering products, and to customize products according to consumer's requests. Equipment manufacturers for reflow soldering use heating factor as an important controlling parameter to establish automatic system for managing solder joint reliability. A reliable soldering result can be achieved using the automatic reflow management system, to control and optimize thermal profile, which leads to the adjustment of the heating factor.

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