Technical Articles

October 25, 2017

By Tim O’Neill, Technical Marketing Manager

Published in CIRCUITS ASSEMBLY

Picking the right tool to prevent electrochemical contaimination at the rework bench.

A half-dozen versions of the same scenario occurred in the past month, all having to do with materials and processes used in post-op/rework applications. This step of the production process often escapes the attention of engineers because there’s no cool machinery or any real engineering that takes place. Most hand-solder operators are highly proficient and have...

June 28, 2017

By Tim O’Neill, Technical Marketing Manager

Published in CIRCUITS ASSEMBLY

With RoHS exemptions set to expire, can SAC305 hang on?

It is not the strongest of the species that survive, nor the most intelligent, but the one most responsive to change.
– Charles Darwin

The final steps of RoHS will be phased in over the next 24 months and once implemented; lead will be virtually eliminated from the solder supply chain for electronic assembly. With the last exemptions applying predominantly to high reliability applications, the materials in use are being scrutinized to determine if they can perform to the mission...

March 13, 2017

By Tim O’Neill, Technical Marketing Manager

Published in CIRCUITS ASSEMBLY

I vividly remember a moment in 1994, sitting in a job interview, trying to conjure an image of the periodic table for the abbreviations for tin (Sn) and lead (Pb). Of course, these weren’t easy guesses because both elements’ abbreviations are derived from their Latin roots: tin from stannum and lead from plumbum. I incorrectly provided my interviewer with the abbreviation for titanium (Ti) and the famously nonexistent unobtainium (Uo). As confused as I was at the time, little did I realize how simple things actually were.

Back then, there was essentially one alloy in use for electronics assembly: Sn63/Pb37. A few specialized applications used a small percentage of...

January 12, 2017

By Tim O’Neill, Technical Marketing Manager

Published in CIRCUITS ASSEMBLY

Would you believe QFN ground pad voids could be cut by over 50% with a zero-cost, super-simple stencil aperture modification? Not a mod to the ground pad apertures where the voiding is problematic, just to the I/O apertures? Neither did we. That’s why we did some deeper digging into what we are now calling the “AIM I/O” aperture modification.

In November’s column, we reported a dramatic reduction in voids when QFN I/O pads were left unpasted, and mentioned our technical staff’s observations and ensuing experiments led us to this new void mitigation technique, but we didn’t explicitly describe the I/O aperture design. It’s a simple...

November 07, 2016

By Tim O’Neill, Technical Marketing Manager

Published in CIRCUITS ASSEMBLY

As I sit in Chicago’s O’Hare Airport having just left another productive and exciting SMTA International trade show, I reflect on what an excellent opportunity this event presents to network and stay current in the world of electronics assembly. If you don’t attend these events regularly, you should. I was fortunate to have the opportunity to attend a number of the technical conference sessions and not only learn what is emerging, but also speak with customers and colleagues on what they see as the most pressing needs of the market.

To sum it up… BTC void reduction. The technical sessions on void reduction I attended were all standing...

August 08, 2016

By Tim O’Neill, Technical Marketing Manager

Published in CIRCUITS ASSEMBLY

We’ve been doing a lot of print testing in our lab. In our first set of published results, “The Impact of Reduced Solder Alloy Powder Size on Solder Paste Print Performance1” from IPC/APEX 2016, we revealed a hierarchy of input variables to maximize solder paste transfer efficiency and minimize variation. In that study, we used a fully-optioned stencil as part of the equipment set. In order to tease out the data we were looking for, we could not lose critical information to the noise of stencil-induced variations.

If the stencil in that study were an automobile, it would be a Bentley. It was made by a consistently top-performing...

April 21, 2016

By Tim O’Neill, Technical Marketing Manager, Carlos Tafoya and Gustavo Rameriez

Abstract

From the Apple™ Watch and body cameras for law enforcement to virtual reality hardware and autonomous transportation, the demands and opportunities for electronics to improve our lives are only limited by our imagination. The capability of existing PCB assembly technology needs to advance rapidly to meet the mission profile of these new devices. The demand common to all of these devices is increased functionality in a smaller space. For the solder paste manufacturer, this path inevitably leads to incorporating finer metal powder into solder paste to facilitate ultra-fine pitch printing. In this study, we will evaluate the benefits and implications of finer mesh solder powder on critical aspects of solder paste performance. 

...

April 13, 2016

By Tim O’Neill, Technical Marketing Manager

Stencil printing is an efficient and effective way of applying millions of well-controlled solder paste deposits, but it is not without its limitations. Many packages, such as area array and bottom termination components, keep getting smaller, while connectors, shields and other big components remain the same size, or grow even larger. Pushing the limits of stencil printing on either or both ends of the printable size spectrum can present considerable challenges for PCB assemblers.

One way to conquer these challenges is to dispense solder paste. Dispensing is an attractive option because it allows for infinite flexibility - it can produce both very small deposits or large deposits and it is fully compatible with the existing SMT process and materials. In fact, many printable solder pastes have dispensable...

February 17, 2016

By Karl Seelig, Vice President Technology and Tim O’Neill, Technical Marketing Manager

The term “squircle” is a portmanteau, or mashup, of square and circle. It’s a real word, and the shape is also known as a superellipse to supernerds. We jest, but besides having a funny name, the squircle is an effective tool for maximizing solder paste release and overall deposit volume.

A squircle (FIGURE 1) is a square with rounded corners that, when incorporated into stencil aperture designs for small area arrays, provides better print quality than either a square or a circle alone. It brings the best of both worlds to an extremely challenging part of the printing process.

...
December 10, 2015

By Karl Seelig, Vice President Technology and Tim O’Neill, Technical Marketing Manager

Viscosity and thixotropy are not words heard in casual conversation, yet they are very common material characteristics we encounter in our everyday lives.

Viscosity is defined as a fluid’s resistance to flow, but is more commonly referred to as a fluid’s “thickness” (flowing slowly like motor oil) or “thinness” (flowing easily, like water). Thixotropy, on the other hand, is a unique property in which viscosity changes with the forces being applied to it in a nonlinear fashion. Thixotropy is a critical characteristic for paint, toothpaste, nail polish and, if you're reading Circuits Assembly, solder paste.

...

September 29, 2015

By Karl Seelig, Vice President Technology and Tim O’Neill, Technical Marketing Manager

Solder paste is an elaborate mixture of metal powders, acids, thixotropes, solvents and a variety of other chemicals. When combined, the reactions and interactions can be extremely varied and complex. When designing solder paste chemistry, key considerations include not only its inprocess performance but how to maintain the stability of that performance against the rigors of time, temperature fluctuations and usage. 

Stencil printing is arguably the critical process on the assembly line...

August 18, 2015

By Karl Seelig, Vice President Technology and Tim O’Neill, Technical Marketing Manager

Solder paste – that ubiquitous, viscous, sticky blob that is applied as the first step of every SMT assembly process – is a surprisingly complex product. It is composed of two primary constituents: solder powder, which accounts for 85% to 90% by weight or 50% by volume, and flux medium as the balance. As complicated as powder development and manufacturing can be, flux medium is even more so, due to the myriad demands and constraints placed on it.

Imagine you are planning a big party and you decide to make the aptly named Patience Cake (FIGURE 1) – arguably one of the most complicated baked goods...

June 12, 2015

By Mehran Maalekian, Yuan Xu, Amir Hossein Nobari, Karl Seelig of AIM Metals & Alloys

Abstract. This paper compares three commercial lead-free solders; CASTIN®, Babbitt and SAC-I and their modified compositions in terms of mechanical and soldering properties. Solders tested are six alloys with different compositions in the range of (major elements): Sn/Cu(0.7-4)/Ag(0-4)/Sb(0.5-8)/Bi(0-3)/Ni(0-0.15). Effects of alloying elements on the thermal behavior (melting and solidification), wetting force, contact angle, spreading, tensile and hardness properties are studied. Based on preliminary results an alloy modification is made and its properties are compared and discussed against the commercial...

May 29, 2015

By Karl Seelig, Vice President Technology and Tim O’Neill, Technical Marketing Manager

From Univac to the latest wearable gadget, electronics keep shrinking. As transistors get smaller, so too do their packaging, solder interconnections, and a key ingredient in making those interconnections: solder powder. Often overlooked on miniaturization roadmaps, the ultrafine particles of metal carried in solder paste play a critical role in solder joint formation, and must be optimized for printing and reflow of subminiature solder joints.

The solder powder manufacturing process is very complex and involves atomizing molten alloy and solidifying the tiny droplets while dispersed in gas. There are many different ways to atomize metallic powders. Most methods are considered...

April 04, 2015

By Karl Seelig, Vice President Technology and Tim O’Neill, Technical Marketing Manager

Nearly every process engineer has found themselves in this quandary: something goes awry with the process, and the supplier finger-pointing begins immediately. With machines, chemistry, components and PCBs all factoring into the mix, it often appears that a supplier’s first line of response is to deflect responsibility rather than help seek the root cause. Chemistry providers don’t have the luxury of suggesting a few mechanical measurements or a quick check under the hood to rule out our products as the source of problems, so we are accustomed to rolling up our sleeves and helping solve them.

We occasionally field calls on solder mask crazing, delaminating or peeling after wave...

February 02, 2015

By Karl Seelig, Vice President Technology and Tim O’Neill, Technical Marketing Manager

We recently received a call from a contract assembler that was fighting solder balls after reflow. They were getting solder balls on one capacitor and tried to address it with profile changes. Sometimes the problem went away, but it always came back. They were also getting blowholes in the same solder joints from time to time.

First, we tried to identify the root cause for the balling problem remotely. The typical questions when confronted with this issue include:

  • On which components are the solder balls occurring?
  • ...
December 01, 2014

By Karl Seelig, Vice President Technology and Tim O’Neill, Technical Marketing Manager

BTCs, or bottom termination components, are a class of package referred to by a variety of acronyms and abbreviations. Different component and packaging companies may use different nomenclature (FIGURE 1), but almost all these components share one common, ugly characteristic: large pads that are prone to solder voiding. By design, these large thermal or ground pads require a defined percentage of contact with the solder and PCB to properly conduct heat and/or electricity. Excess solder voids can impact performance and reliability of the package.

The voiding problem has given both designers and manufacturers heartburn for the better part of two decades. Some of the...

September 02, 2014

By Karl Seelig, Vice President Technology, Tim O’Neill, Technical Marketing Manager and Mehran Maalekian, R&D Manager

Silver is a known whisker promoter but small amounts of bismuth mitigate the problem.  Alloy composition has a strong influence on tin whisker production and has proven to either mitigate or exacerbate the propensity for a solder to whisker. In our year-long study of the relationship between alloy composition on tin whisker formation, SAC 305 notoriously produced more and larger whiskers than any of the other alloys tested.

Sn0.6Ag0.6Cu3Bi, labeled “Alloy #69-2” in our test matrix, a tweak on one of...

July 01, 2014

By Karl Seelig, Vice President Technology, Tim O’Neill, Technical Marketing Manager and Mehran Maalekian, R&D Manager

Phase 2 of our study involved wetting balance, spread, DSC and mechanical tests. We’re continuing our summary of a year-long experiment aimed at identifying lead-free solder alloys that mitigate tin whisker growth. This study cut right to the chase, beginning with an elimination round. The first phase knocked out two-thirds of the nine original candidate alloys based on their whisker production.

The results of the tests were both intriguing and enlightening, and forced us to rethink what we thought we knew about tin whisker...

June 30, 2014

By Karl Seelig, Vice President Technology and Tim O’Neill, Technical Marketing Manager

Abstract. The drive to reduced size and increased functionality is a constant in the world of electronic devices. In order to achieve these goals, the industry has responded with ever-smaller devices and the equipment capable of handling these devices. The evolution of BGA packages and leadless devices is pushing existing technologies to the limit of current assembly techniques and materials.

As smaller components make their way into the mainstream PCB assembly market, PCB assemblers are reaching the limits of Type 3 solder paste, which is currently in use by most manufacturers.

The goal of...

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