Technical Articles From Indium Corporation

D-PAK Voiding: A Study to Determine the Origins of D-PAK Voiding

Dec 29, 2020 | Kim Flanagan and Greg Wade

Voiding in bottom termination components (BTCs) like QFNs and LGAs have become quote the hot topic in the SMT industry. Surprisingly, one type of BTC component that is observed to have excessive amounts of voiding is the DPAK. One would think that a component with leads located on only one side would mitigate flux entrapment and allow outgassing to escape more easily from beneath the component, as compared to other BTCs where the component is affixed to the PCB on two or more sides. However, the exact opposite has been observed in most cases....

The Risk And Solution For No-Clean Flux Not Fully Dried Under Component Terminations the Risk And Solution For No-Clean Flux Not Fully Dried Under Component Terminations

Nov 24, 2020 | Fen Chen and Ning Cheng Lee, Ph.D.

The miniaturization trend is driving industry to adopting low standoff components or components in cavity. The cost reduction pressure is pushing telecommunication industry to combine assembly of components and electromagnetic shield in one single reflow process. As a result, the flux outgassing/drying is getting very difficult for devices due to poor venting channel. This resulted in insufficiently dried/burnt-off flux residue. For a properly formulated flux, the remaining flux activity posed no issue in a dried flux residue for no-clean process. However, when venting channel is blocked, not only solvents remain, but also activators could not be burnt off. The presence of solvents allows mobility of active ingredients and the associated corrosion, thus poses a major threat to the reliability. In this work, a new halogen-free no-clean SnAgCu solder paste, 33-76-1, has been developed. This solder paste exhibited SIR value above the IPC spec 100 MΩ without any dendrite formation, even with a wet flux residue on the comb pattern. The wet flux residue was caused by covering the comb pattern with 10 mm × 10 mm glass slide during reflow and SIR testing in order to mimic the poorly vented low standoff components. The paste 33-76-1 also showed very good SMT assembly performance, including voiding of QFN and HIP resistance. The wetting ability of paste 33-76-1 was very good under nitrogen. For air reflow, 33-76-1 still matched paste C which is widely accepted by industry for air reflow process. The above good performance on both non-corrosivity with wet flux residue and robust SMT process can only be accomplished through a breakthrough in flux technology....

Voiding Performance with Solder Pastes Containing Modified SAC Alloys for Automotive Applications in Bottom Terminated Component Assemblies

Jul 24, 2019 | Brook Sandy-Smith

Voiding is a key concern for components with thermal planes because interruptions in Z-axis continuity of the solder joint will hinder thermal transfer. When assembling components with solder paste, there is a high propensity for voiding due to the confined nature of the solder paste deposits under the component. Once reflowed, many factors contribute to the amount of voiding in a solder joint such as the reflow profile, designs of the component, board and stencil, and material factors. This study will focus on the solder paste alloy and flux combination as well as profile and board surface finishes....

Process Optimization for Fine Feature Solder Paste Dispensing

Dec 19, 2018 | Maria Durham, Greg Wade, and Brandon Judd; Indium Corporation, John Boggiatto; ITW EAE - Speedline Technologies

With the rapid trend towards miniaturization in surface mount and MEMs lid-attach technology, it is becoming increasingly challenging to dispense solder paste in ultra-fine dot applications such as those involving chip capacitors or BGA packages, as well as dispensing ultra-fine lines in MEMs lid-attach applications. In order to achieve ultra-fine dots and fine line widths while dispensing solder paste, both the solder material and dispensing equipment need to be optimized. Optimizing the equipment can be very challenging, as there are many input variables that can affect the dispense quality of the solder paste. In this paper we will evaluate the many equipment variables involved in the solder paste dispensing process, and the impact these variables have on the dispense quality of the solder paste....

Understanding the Effect of Different Heating Cycles on Post-Soldering Flux Residues and the Impact on Electrical Performance

Nov 20, 2018 | Brook Sandy-Smith, Indium Corporation and Terry Munson, Foresite Inc.

There are several industry-accepted methods for determining the reliability of flux residues after assembly. The recommended methods of test sample preparation do not always closely mimic the thermal cycle experienced by an assembly. Therefore, extraction from actual assemblies has become a popular method of process control to assess consistency of post-reflow cleanliness. Every method of post-reflow flux residue characterization will depend on the reflow process followed to prepare the coupon.

This investigation will focus on the effect of thermal conditions on the remainder of active ingredients in flux residues after assembly with no-clean solder pastes....

Does Thermal Cycling Impact the Electrical Reliability of a No-Clean Solder Paste Flux Residue

Aug 29, 2018 | Eric Bastow

No-clean solder pastes are widely used in a number of applications that are exposed to wide variations in temperature during the life of the assembled electronics device. Some have observed that cracks can and do form in flux residue and have postulated that this is the result of or exacerbated by temperature cycling. Furthermore, the potential exists for the flux residue to soften or liquefy at elevated temperatures, and even flow if orientated parallel to gravity. In situations such as in automotive electronics, where significant temperature cycling is a reality and high reliability is a must, concern sometimes exists that the cracking and possible softening or liquefying of the residue may have a deleterious effect on the electrical reliability of the flux residue. This paper will attempt to address this concern....

A Novel Solution for No-Clean Flux not Fully Dried under Component Terminations

Aug 17, 2017 | Dr. Ning-Cheng Lee & Fen Chen

At SMT assembly, flux outgassing/drying is difficult for devices with poor venting channel, and resulted in insufficiently dried/burnt-off flux residue for no-clean process.

Examples including:

• Large low stand-off components such as QFN, LGA
• Components covered under electromagnetic shield which has either no or few venting holes
• Components assembled within cavity of board
• Any other devices with small open space around solder joints

A Novel Epoxy Flux On Solder Paste For Assembling Thermally Warped POP

Aug 17, 2017 | Ming Hu, Lee Kresge, and Ning-Cheng Lee

A novel epoxy flux EF-A was developed with good compatibility with no-clean solder pastes, and imparts high reliability for BGA assembly at a low cost. This compatibility with solder pastes is achieved by a well-engineered miscibility between epoxy and no-clean solder paste flux systems, and is further assured with the introduction of a venting channel. The compatibility enables a single bonding step for BGAs or CSPs, which exhibit high thermal warpage, to form a high-reliability assembly. Requirements in drop test, thermal cycling test (TCT), and SIR are all met by this epoxy flux, EF-A. The high viscosity stability at ambient temperature is another critical element in building a robust and userfriendly epoxy flux system. EF-A can be deposited with dipping, dispensing, and jetting. Its 75°C Tg facilitates good reworkability and minimizes the adverse impact of unfilled underfill material on TCT of BGA assemblies....

Establishing a Precision Stencil Printing Process for Miniaturized Electronics Assembly

Jun 13, 2017 | Chris Anglin

The advent of miniaturized electronics for mobile phones and other portable devices has required the assembly of smaller and smaller components. Currently 01005 passives and 0.3 mm CSPs are some of the components that must be assembled to enable these portable electronic devices. It is widely accepted that about 65% of all end of the line defects occur in the stencil printing process. Given all of the above, it is critical that a precision stencil printing process be developed to support miniaturized electronic assembly.

This paper is a summary of a significant amount of experimental data and process optimization techniques that were employed to establish a precision SMT printing process....

Can Age and Storage Conditions Affect the SIR Performance of a No-Clean Solder Paste Flux Residue?

Feb 09, 2017 | Eric Bastow

The SMT assembly world, especially within the commercial electronics realm, is dominated by no-clean solder paste technology. A solder paste flux residue that does not require removal is very attractive in a competitive world where every penny of assembly cost counts. One important aspect of the reliability of assembled devices is the nature of the no-clean solder paste flux residue. Most people in this field understand the importance of having a process that renders the solder paste flux residue as benign and inert as possible, thereby ensuring electrical reliability.

But, of all the factors that play into the electrical reliability of the solder paste flux residue, is there any impact made by the age of the solder paste and how it was stored? This paper uses J-STD-004B SIR (Surface Insulation Resistance) testing to examine this question....

Understanding SIR

Feb 06, 2014 | Chris Nash, Technical Support Engineer, Eric Bastow, Senior Technical Support Engineer; Indium Corporation.

Many electronics manufacturers perform SIR testing to evaluate solder materials and sometimes the results they obtain differ significantly from those stated by the solder material provider. The difference in the results is typically the result of SIR coupon preparation. This paper will discuss the issue of SIR coupon preparation, board cleaning techniques, and how board cleanliness directly affects SIR results....

Addressing the Challenge of Head-In-Pillow Defects in Electronics Assembly

Dec 27, 2013 | Mario Scalzo Senior Technical Support Engineer CSMTPE, Six-Sigma Black Belt

The head-in-pillow defect has become a relatively common failure mode in the industry since the implementation of Pb-free technologies, generating much concern. A head-in-pillow defect is the incomplete wetting of the entire solder joint of a Ball-Grid Array (BGA), Chip-Scale Package (CSP), or even a Package-On-Package (PoP) and is characterized as a process anomaly, where the solder paste and BGA ball both reflow but do not coalesce. When looking at a cross-section, it actually looks like a head has pressed into a soft pillow. There are two main sources of head-in-pillow defects: poor wetting and PWB or package warpage. Poor wetting can result from a variety of sources, such as solder ball oxidation, an inappropriate thermal reflow profile or poor fluxing action. This paper addresses the three sources or contributing issues (supply, process & material) of the head-in-pillow defects. It will thoroughly review these three issues and how they relate to result in head-in pillow defects. In addition, a head-in-pillow elimination plan will be presented with real life examples will be to illustrate these head-in-pillow solutions....

Best Practices Reflow Profiling for Lead-Free SMT Assembly

Jun 05, 2013 | Ed Briggs and Ronald C. Lasky, Ph.D., PE.

The combination of higher lead-free process temperatures, smaller print deposits, and temperature restraints on electrical components has created difficult challenges in optimizing the reflow process. Not only are the electronic components and the PWB at risk, but the ability to achieve a robust solder joint becomes difficult, especially if the PCB is thermally massive. In addition, the constant miniaturization of electronic components, hence smaller solder paste deposits, may require the use of smaller particle-sized powders (...) This paper is a summary of best practices in optimizing the reflow process to meet these challenges of higher reflow temperatures, smaller print deposits, decreased powder particle size, and their affect on the reflow process....

No-Clean Flux Residue and Underfill Compatibility Effects on Electrical Reliability

Apr 11, 2013 | Eric Bastow

With the explosion of growth in handheld electronics devices, manufacturers have been forced to look for ways to reinforce their assemblies against the inevitable bumps and drops that their products experience in the field. One method of reinforcement has been the utilization of underfills to "glue" certain SMDs to the PCB. Bumped SMDs attached to the PCB with a no-clean soldering process offer the unavoidable scenario of the underfill coming in contact with a flux residue. This may or may not create a reliability issue... First published in the 2012 IPC APEX EXPO technical conference proceedings...

Advantages of Bismuth-based Alloys for Low Temperature Pb-Free Soldering and Rework

Dec 20, 2012 | Brook Sandy, Edward Briggs and Ronald Lasky, Ph.D.

The increased function of personal electronic devices, such as mobile phones and personal music devices, has driven the need for smaller and smaller active and passive components. This trend toward miniaturization, occurring at the same time as the conversion to RoHS-compliant lead-free assembly, has been a considerable challenge to the electronics assembly industry. The main reason for this is the higher reflow process temperatures required for Pb-free assembly. These higher temperatures can thermally damage the PCB and the components. In addition, the higher reflow temperatures can negatively affect the solder joint quality, especially when coupled with the smaller paste deposits required for these smaller components. If additional thermal processing is required, the risk increases even more. First Published at SMTA's International Conference on Soldering and Reliability in Toronto, May 2011...

Minimizing Voiding In QFN Packages Using Solder Preforms

Jul 27, 2012 | Seth J. Homer, Ronald C. Lasky, PhD, PE

First published in the 2012 IPC APEX EXPO technical conference proceedings. The focus of this paper will quantify the preform requirements and process adjustments needed to use preforms in a standard SMT process. In addition, experimental data showing vo...

RoHS: Five Years Later

Dec 01, 2011 | Dr Ronald C. Lasky

Are electronics any “greener” than before RoHS? It is a fair question to ask. With the advent of RoHS on July 1, 2006, and more recently REACH, one might be inclined to answer that it is greener than it was. We will take a look at this question in several...

A Review of Test Methods and Classifications for Halogen-Free Soldering Materials

Jun 23, 2011 | Jasbir Bath, Gordon Clark, Tim Jensen, Renee Michalkiewicz, Brian Toleno

Over the last few years, there has been an increase in the evaluation and use of halogen-free soldering materials. In addition, there has been increased scrutiny into the level of halogens and refinement of the definition and testing of halogen-free solde...

Voiding Control for QFN Assembly

Apr 07, 2011 | Derrick Herron, Dr. Yan Liu, and Dr. Ning-Cheng Lee

Quad Flat No Leads (QFN) package designs receive more and more attention in electronic industry nowadays. This package offers a number of benefits including (1) small size, such as a near die-sized footprint, thin profile, and light weight; (2) easy PCB t...

Dispelling 10 Myths About Nitrogen Reflow

Jan 27, 2011 | Dr. Andy Mackie

In this paper, we will talk about reflow in an enclosed oven, although many of these discussions may pertain to wave soldering and even vacuum soldering.....

Leaded and Lead-Free Solder Paste Evaluation Screening Procedure

May 12, 2010 | Ronald C. Lasky, Ph.D., PE; Indium Corporation of America Daryl Santos, Ph.D., Aniket A. Bhave; Binghamton University

Numerous studies have shown that greater than 60% of end of line defects in SMT assembly can be traced to solder paste and the printing process. Reflowing adds another 15% or so. In light of this fact, it is surprising that no simplified procedure for solder paste evaluation has been documented. This paper is about such a procedure....

An Effective Design of Experiment Strategy to Optimize SMT Processes

Apr 22, 2010 | Ronald C. Lasky, Ph.D., PE, Professor Daryl Santos, Ph.D., Joseph R. Cloyd

It is now widely accepted that using designed experiments is the most effective way to optimize surface mount technology (SMT) processes. This situation begs the question "what is an effective strategy in implementing this powerful tool?" This paper will present such a strategy that incorporates Taguchi's approach for screening, full factorial analysis for optimization and central composite design for precise modeling. We will present these techniques using MINITABTM Release 13 statistical software and printed circuit board industry applications....

Aiming for High First-pass Yields in a Lead-free Environment

Mar 04, 2010 | Mario Scalzo Senior Technical Support Engineer CSMTPE, Six Sigma Black Belt, Indium

While the electronics manufacturing industry has been occupied with the challenge of RoHS compliance and with it, Pb-free soldering, established trends of increasing functionality and miniaturization have continued. The increasing use of ultra-fine pitch and area-array devices presents challenges in both printing and flux technology. With the decrease in both the size and the pitch of said components, new problems may arise, such as head-in-pillow and graping defects...

The Basics of Soldering

Dec 14, 2009 | Chris Nash, Indium Corporation

In this article, I will present a basic overview of soldering for those who are new to the world of soldering and for those who could use a refresher. I will discuss the definition of soldering, the basics of metallurgy, how to choose the proper alloy, the purpose of a flux, soldering temperatures, and typical heating sources for soldering operations....

Solder Preform Basics

Dec 14, 2009 | Paul A. Socha, Indium Corporation.

Solder paste is the most recognized form of solder used in electronics assembly today. A surface mount application depends on solder paste to attach the components to the circuit board. However, solder paste may not be the only solution. This is especially true when working with through-hole components or very large devices that require more solder than can be supplied by printed solder paste. In fact, quite often a PCB involves mixed technology that requires more than one form of solder. Solder paste is used for the surface mount components and solder preforms are utilized to attach the leads on through-hole components, avoiding wave or selective soldering....

Thermal Profiling: A Practical Approach to Reflow Profiling

Dec 14, 2009 | Liyakathali Koorithodi, Indium Corporation

In the lead-free era, thermal profiling has a critical role in the SMT assembly process. We discuss the profiling, tools, practical issues, and inspection methods of golden boards, and related tools. As the process window narrows, profiling equipment and/or thermocouple (TC) errors must be taken into consideration. In addition, the accuracy and attachment method of the thermocouple will significantly impact critical assemblies....

A Compliant and Creep Resistant SAC-Al(Ni) Alloy

Mar 27, 2009 | Dr. Benlih Huang, Dr. Hong-Sik Hwang, and Dr. Ning-Cheng Lee; Indium Corporation of America.

The Sn-Ag-Cu (SAC) alloys have been considered promising replacements for the lead-containing solders for the microelectronics applications. However, due to the rigidity of the SAC alloys, compared with the Pb-containing alloys, more failures have been found in the drop and high impact applications for the portable electronic devices, such as the personal data assistant (PDA), cellular phone, notebook computer..etc...