White Paper Vault
Solder Connection distribute products manufactured by AIM Electronics and AIM Industrial. Ranging from Solder Pastes and Fluxed Solder Wires for the Electronics Market to Casting Alloys from Figurine manufacturing and Solid Solder Wire for Stained Glass.
Technical Papers
Download a selection of AIM Technical Papers to ensure you stay up to date with the latest industry trends and research.
Addressing Low-Temperature Rework Concerns
ABSTRACT Implementation of low-temperature solders has been a subject of considerable interest for many consumer electronics manufacturers. Low-temperature solders represent a significant material and process cost advantage over traditional silver-bearing and low-silver alloys. Bismuth-containing alloys enable low-melting temperatures; therefore, if the mission profile of an assembly tolerates the limitations of bismuth-containing low-temperature solders, implementation is favorable.
Effect of Under-stencil Wipe Chemistry on Print Performance
Can a change of solvent in the printer improve SMT printing?
ANY ENGINEER WILL TESTIFY lab testing may not correlate with field results. Laboratory data are developed under ideal conditions to generate accurate and repeatable data, whereas a production setting introduces variables not reproducible in the lab environment.
In this report, AIM’s application lab approximated a production environment in a multi-hour printing test to quantify the effect of under-stencil wipe solvent on solder paste performance. This experiment compared isopropyl alcohol (IPA) and a novel stencil cleaner. IPA is not recommended as an in-process stencil cleaner, but is often used because it is inexpensive, effective and readily available. However, IPA is not a constituent of solder pastes and can therefore cause changes to paste that will negatively impact performance.
Is SMT Ready for Low-Temperature Solders?
With no standard in sight, emerging alloys require unique fluxes and processes.
LOW-TEMPERATURE SOLDERING is a subject of considerable interest and development. Several forces are driving implementation of solders with lower peak reflow temperatures than SAC 305 and its variants. The most technically significant is reduced warping of component and substrates. Chip suppliers are particularly interested in lower reflow temperatures, as thinner components are needed to meet dimensional limitations of thinner, smaller and faster devices. When a component deforms during reflow, the solder interconnect may be compromised, resulting in non-wet opens (NWO). NWO defects are difficult to detect and may not manifest until after a product is in the field. Other advantages of low-temperature soldering include the incorporation of lower-cost plastics, component and laminate materials, and reduced energy consumption and related environmental…
Solder Paste is Dumb
Could vendor collaboration get to the root cause of an intermittent soldering problem?
Simply put, the ultimate function of a PCB assembly line is to create millions of solder joints without error. This task is complicated by the myriad materials that come together during assembly, and relies on the quality of each lead, pad and sphere to be soldered. When a soldering defect is discovered, it is common practice to presume the soldering materials are the cause, which seems logical, considering it is a solder defect. This assumption is often misplaced. This scenario plays out regularly, as illustrated in a recent case submitted to our failure analysis team for diagnosis.
Profiles in Expertise
Is reflow the only process where the outcome could be impacted in real-time?
One of AIM’s field engineers came back from a cross-country trip this week with stories of a profiling issue that was giving the client difficulties. Ultimately, the issue was design-related with a large ΔT that could not be overcome with the equipment used in production. It took a full day of attempts to make that final assessment.
Many engineers and technicians I work with rank reflow profiling alongside getting their teeth cleaned or an early morning workout. You know you need to do it, and the benefits are significant, but they aren’t immediate, and it is an unpleasant chore. Let’s take a minute to go over best practices for reflow profiling. Ideally, a “golden board” will have been supplied as part of the work kit by your customer or your design team. This…
Mr. Clean
Picking the right tool to prevent electrochemical contamination 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 developed techniques that get the job done, which can lull a supervisor or production manager into a false sense of…
Life After SAC
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 DarwinThe 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 requirements of high reliability PCB. Concurrent to this material concern, is the unrelenting trend in…
Solder Alloy Fragmentation
With RoHS exemptions set to expire, the SMT market might see a host of new solders.
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 silver (Ag) in the SnPb, tin-silver or high-lead solders, and a handful of old-timers wouldn’t…
Aperture Design to Minimize QFN Voiding
Stop Tweaking the Ground Pad Prints; Start Tweaking the I/O Prints.
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 before introducing it.
On the Tech Tips, we reported a dramatic reduction in voids when QFN I/O pads were left unpasted, but doesn’t stop there, that observation lead and experimentation lead us to an effective and repeatable void reduction technique, but we didn’t tell you exactly what that I…
Void Reduction on QFNs
Sometimes the answers to the most tenacious questions are right under your nose.
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 room only, and the topic was the subject of many hallway conversations among technologists. The presentations offered supplier and user…
Pretty Slick
STENCILS: Coated vs. Uncoated… what’s better for the process?
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 Performance” from IPC/APEX, 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-…
The Impact of Reduced Alloy Powder Size on Solder Paste Print Performance
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.
Type IV, V, VI SAC305 solder powder will be tested and their characteristics in several key areas will be measured and studied. The key variables will be print…
The Bigger the Blob, the Easier the Job
Stencil printing is efficient and effective, but it is not without its limitations.
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…
Squaring the Circle
Or what the @#$% is a squircle, and what is it doing on my stencil?
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.
Go with the Flow
Paste viscosity can inform why solder performs differently under different conditions.
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…
Unforgiving Environments
Proper handling and storage controls go a long way toward print quality.
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 because it lays the foundation for the entire assembly. A quality print does not necessarily preclude rework, but a bad print effectively guarantees it. Additionally, the PCB assembly process is vulnerable to external influences, such as operating environments, setup changes and operator…
The Balancing Act
In Search of the Perfect Solder Paste. Hint, it’s a moving target.
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 recipes imaginable. Different batches of batter must be mixed in advance, refrigerated overnight and baked in individual pans. Pieces of the baked goods are then precision cut, and evenly…
Comparing Mechanical and Soldering Properties of Alternative Lead-Free Alloys
Comparing Properties of CASTIN™, BABBITT & Alternative Lead-Free 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 creep resistant solder alloy, i.e. SAC-I.
Solder Paste Powder: When to Downsize
A finer type solder paste may solve one problem only to create another.
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 proprietary and are rarely discussed in public forums. A solder paste’s flux and its attributes garner a…
Flux-Crazed Solder Mask
To err is human; to blame the other vendor is… policy.
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.
Head-in-Pillow BGA Defects
Head-in-pillow (HiP), also known as ball-and-socket, is a solder joint defect where the solder paste deposit wets the pad, but does not fully wet the ball. This results in a solder joint with enough of a connection to have electrical integrity, but lacking sufficient mechanical strength. Due to the lack of solder joint strength, these components may fail with very little mechanical or thermal stress. This potentially costly defect is not usually detected in functional testing, and only shows up as a failure in the field after the assembly has been exposed to some physical or thermal stress.
Head-in-pillow defects have become more prevalent since BGA components have been converted to lead-free alloys. The defect can possibly be attributed to chain reaction of events that begins as the assembly reaches reflow temperatures. Components generally make contact with solder paste during initial placement, and start to flex or warp during heating, which may cause some individual solder…
Halogen-Free Assemblies Testing
The increased interest in halogen-free assemblies is a result of Non-Government Organizations (NGOs) exerting pressure on electronic equipment manufacturers to eliminate halogens. The NGOs primary focus is on resolving global environmental issues and concerns. As a result of an increase in the enormous “e-waste” dump sites that have begun showing up around the world, NGOs are pushing consumer electronic manufacturers to ban halogen-containing material in order to produce “green” products. Not only are these sites enormous, but the recycling methods are archaic and sometimes even illegal. This stockpiling and dumping has created growing political and environmental issues. In order to deal with this issue, the question of why halogens are a focal point must be addressed.
As a safety measure halogens are added to organic materials as a fire retardant. The common halogens used only give off bromides with elevated temperatures, decomposing and…
Considerations for Lead-Free Wave Soldering
When converting to lead-free wave soldering, several important business decisions need to be made. The first decision pertains to the wave solder pot. Wave solder pots designed specifically for lead-free soldering are resistant to tin corrosion, contain higher-grade stainless steal components, and typically contain lightweight titanium hardware such as nuts and bolts designed to float rather than sink if dropped in the solder pot. It is well understood that Sn-Ag-Cu alloys are aggressive toward the materials found in many older wave solder machines. If implementing a Sn-Ag-Cu alloy for wave soldering, it is recommended that a new wave solder machine, or at the very least a new solder pot, is part of your expenditure.
Lower-budget operations and/or those that currently have a relatively new wave machine that is not fully depreciated may want to continue using current wave soldering equipment after lead-free soldering has been implemented….
Considerations for Printing Lead-Free Solder Pastes
Abstract. SMT printing will require reexamination and process adjustment when lead-free soldering is implemented. If a high quality solder paste is used and standard rules for SMT printing are followed, consistent stencil life, aperture release, print definition, high-speed print capabilities and print repeatability may be expected.
A Tale of Fresh Eyes: Troubleshooting Chip Component Solder Balls
A Tale of Fresh Eyes, Red Herrings and Dirty Tweezers…
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?
- Are the defects consistently in the same spot/component, or do their locations vary?
- Was the solder paste fresh and permitted to warm to room…
Minimizing BTC Voids
And why waiting until the last process step is a bad idea.
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 drivers for this frustration are that voiding rates are highly variable, and numerous factors can impact their formation. While there is still…
Tin Whiskers Revelations: Part I
A multi-part study found plenty of whiskers, but not where they were expected.
THE ELUSIVE TIN WHISKER is only 1/100th the width of a human hair, but this tiny, single filament protrusion can wreak havoc with all sorts of electronics, and has even been cited as the cause of some sudden acceleration failures in cars. Tin whiskering is not a new phenomenon, however. It has been documented as far back as the 1940s, so why the heightened concern now? Lead was a great mitigator of whiskers and its removal from electronic solder opened the door for increased whisker proliferation, perhaps with sometimes deadly consequences.
Despite years of study, a single root-cause mechanism on whisker formation has yet to be established. Common wisdom suggests that they are a form of stress-relief, compensating for the compressive stresses induced by…
Tin Whiskers Revelations: Part II
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 propagation. The investigation focused on the conventional wisdom that tin whiskers are the result of compressive stresses caused by electroplating, bending, intermetallic growth, and thermal expansion mismatches.
Tin Whiskers Revelations: Part III
Tin Whisker Study Conclusions.
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 the original nine alloys, produced the least and smallest whiskers. It also performed well in the other electronic solder suitability tests such as wetting, oxidation resistance, melting temperature and mechanical properties.
Assessing the Impact of T4 Solder Powder on Print Transfer Efficiency
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 this study is to determine the impact on solder volume deposition between Type 3, Type 4 and Type 5 SAC305 alloy powder in combination with stainless steel laser cut, electroformed and the emerging laser cut nano-coated stencils. Leadless QFN and μBGA components will be the focus of the test utilizing…
J-STD-004B: A New Twist on an Old Standard?
Before rejecting a flux, be sure you understand the standard.
J-STD-004 was updated about five years ago, but the comingling of designations from the old (A) and new (B) revisions in industry literature has created much confusion among users. What changed, what didn’t, how does it affect flux selection criteria, and what does a user need to know? Here’s a quick overview:
Flux designation has three components. The first two letters, RO, RE or OR, represent the basic chemical composition: rosin-based, resin-based or organic acid-based. Nothing has changed there. But the next component to flux designation, L, M or H, which describes the flux’s activity level as low…
The Reflow Limbo: How Low Can We Go?
Sn/Cu/Ni soldering performance at low temperatures.
Nickel-modified tin-copper solder, known commercially as SN100C®, is a leading lead-free alloy for PTH soldering, rework and hot air leveled PCB final finishes. Because it contains no silver, it is much more economical than SAC alloys containing 1, 3 or even 4 percent of the precious metal, and it produces smooth, shiny, easy-to-inspect solder joints. Why has it not gained major acceptance as an SMT alloy? In large part, fear. Fear of full compatibility with SAC reflow processes.
SnCuNi melts at 227°C. SAC305 begins to melt at 217°C, reaching its fully liquid state at approximately 220.6°C. Recommended reflow temperatures are typically at least 13°C higher than melting temperatures; hence the SAC305 peak temperature window of 233 – 255. Applying the 13-degree guideline to the…
Production Testing of Ni-Modified Sn/Cu Solder Paste
ABSTRACT. Low-silver and no-silver lead-free PCB solder alloys represent substantial cost savings over SAC alloys that contain 3% silver. Many wave solder operations use silver-free alloys for through hole soldering, and SMT operations are also beginning to adopt the alloy for surface mount soldering.
This paper reviews two case studies that test Ni-modified SnCu solder paste on mixed technology circuit assemblies which currently use SAC305 in production. The major differentiator between the two cases is the reflow profile: In one case, the SAC profile was considered nearly perfect for the SnCuNi alloy, peaking at 245°C. In the other case, thermally sensitive components constrained the profiles to peaking near 235°C, only 8 degrees above the silver-free alloy’s 227°C melting temperature. This important case is used to explore the lower limit of reflow capability and compare it…
Whats on Your Rework Bench
Every seasoned SMT process engineer has at least one nightmare story about bad rework chemistry. Whether it’s the wrong flux sneaking into the operation, underprocessed flux remaining on the board, or improper residue removal, they all risk the same inglorious fate: field failure. While rework operators and process engineers rarely get a glimpse of the long-term damage of inappropriate materials or processes, the Failure Analysis engineers see it all. They report that the vast majority of solder-related issues are on reworked solder joints, and the lion’s share of those is due to the rework chemistry.
How does the wrong flux work its way into rework? Simple human error. In some cases, operators who experience difficulty using approved rework fluxes on parts with poor solderability bring in more active materials from their personal collections. In auditing rework stations, we’ve found all sorts of unapproved soldering fluxes…
Conformal Coating Over No Clean
Introduction. As the proliferation of modern day electronics continues to drive miniaturization and functionality, electronic designers/assemblers face the issue of environmental exposure and uncommon applications never previously contemplated.
This reality, coupled with the goal of reducing the environmental and health implications of the production and disposal of these devices, has forced manufacturers to reconsider the materials used in production.
Furthermore, the need to increase package density and reduce costs has led to the rapid deployment of leadless packages such as QFN, POP, LGA, and Micro-BGA. In many cases, the manufacturers of these devices will recommend the use of no clean fluxes due to concerns over the ability to consistently remove flux residues from under and around these devices.
Not All WOA (Weak Organic Acids) Are the Same
Abstract. In an effort to reduce volatile organic compound (VOC) emissions within our environment, policymakers have encouraged and/or mandated that electronics manufacturers change from alcohol-based VOC-containing fluxes to water-based VOC-free flux alternatives. As a result, the use of VOC-free fluxes is growing throughout North America, Asia and Europe.
The purpose of this study is to explain several factors relating to the use of a VOC-free flux in the soldering process and their impact on testing and product reliability. These factors include; the effect of varying types of acids used in flux formulations and their impact on Ion Chromatography (IC) and Surface Insulation Resistivity (SIR) test results and weak organic acids (WOA) solubility and their influence on the electrical integrity of assemblies. This paper shall provide valuable insight into the outcome of acid-solvent interactions.
Lead-Free Alloy Development
Abstract. When lead-free solders were first introduced to the electronics industry in the early 1990’s, the tin-silver alloy composed of Sn96.5/3.5Ag was the first investigated. The most obvious difference from the industry standard was the substantially higher melting temperature of 221°C versus 183°C (Sn63/Pb37).
Although Sn/Ag had been used extensively in hybrid electronics, concerns over silver migration and silver creep drove the industry to investigate Sn/Cu and (S)n/(A)g/(C)u (SAC) alloys. Initial selection criteria deemed SAC to be the more reliable option. In early tests, Sn/Cu exhibited inferior reliability in thermal cycling (-65+125C) and was prone to in-process wetting issues. The three leading commercialized SAC alloys were introduced as SAC305, SAC387, and SAC405. (Note: the first number refers to silver content followed by the last number, which is the copper content. SAC305 is tin, 3% silver and 0.5% …
Overcoming the Challenges of the QFN
Introduction. Over the last several years, the electronics assembly industry has witnessed a seismic shift toward component miniaturization. Consumer demands for more functionality in smaller packages have motivated OEMs and Contract Manufacturers to engage in new and innovative technologies. As technological advances usher in a more compact design, a decrease in available board space and more densely populated PCB’s have become increasingly common. In response to these demands, the industry has witnessed a proliferation of Quad Flat No Leads (QFN) packages. The goal of this study is to identify the advantages and challenges that the QFN package brings to the electronics assembly process. This paper will also discuss the results of data evidencing the fundamental steps required to successfully implement QFN technology into an assembly.
Bar Solder Drossing Characteristics and Wave Contamination
Solder is a combination of metals that form an alloy with a melting point lower than any of the individual combined elements.
In the process of alloying, the metals are added and melted together and then cooled to a predetermined point above the melting point of the alloy. In the case of electronic-grade tin-lead (Sn63/Pb37) bar, this would be a point above 183°C (361°F) and for a leadfree alloy such as SAC305 (Sn96.5/Ag3.0/Cu0.5) it would be a point above 217-219°C (423-426°F). When an alloy is melted, the surface of the alloy is exposed to air. This interaction of the air on the alloy surface forms an oxide layer called dross. The density of the dross and the alloy are very similar, which causes a slow separation of the two. Typically, dross is not related to impurities but is more related to oxidation rates (although some impurities such…
Controlling Copper Build Up In Automatic Soldering Equipment
Abstract. Since “nothing solders like solder”, HAL (Hot Air Leveling) will continue to hold a significant place in the surface finishing industry. Furthermore, the wave soldering process will continue to be a viable means of electronics assembly. However, as automatic soldering processes using lead-free alloys have become increasingly prevalent, questions have arisen about copper dissolution into these alloys.
A Comparison of Tin-Silver-Copper Lead-Free Alloys
Abstract. As the electronics industry begins to focus upon the tin-silver-copper family of alloys as a viable replacement for tin-lead solders, research needs to be done to determine if any particular alloy is best suited for the broadest range of applications. The tin-silver-copper family of alloys has earned a great deal of positive response from various industry consortia and organizations in recent years and the majority of manufacturers plan on implementing one of these alloys. However, as there are several different alloy formulations within the tin-silver-copper family, background information is necessary to determine which alloy is best suited for the broadest range of applications.
A Study of Lead-Free Wave Soldering
Discussion. As lead-free wave soldering becomes increasingly prevalent, questions have arisen about copper dissolution into lead-free alloys. Concerns have arisen over the use of alloys that may require more solder pot maintenance due to their high copper dissolution rates.
The first part of this study was performed to determine if there is any significant difference between Sn/Ag/Cu alloys. The study compared Sn/Ag3/Cu0.5 (LF218) to Sn/Ag2.5/Cu0.8/Sb0.5 (CASTIN). The purpose was to determine if at wave soldering temperatures one alloy will absorb less copper than the other alloy.
Specialty Solders: A Study of Indium/Lead
More complicated electronics will require the increased use of specialty solders. Specialty solders, such as indium alloys, offer advantages for gold soldering, step soldering and fatigue resistance.
Indium/Lead Solders on Gold. Because they do not leach or dissolve gold as readily as tin/lead solders, indium/lead solders are recommended for soldering to gold. As seen in fig. 1, the phase diagrams of tin/gold shows that tin dissolves approximately 18 percent by weight of gold at soldering temperatures of 225-250°C.1 Under the same conditions the indium/gold phase diagram shows dissolution of only 2 to 4 percent of gold in indium. Thus, with a substantial reduction in the dissolution of gold, less intermetallics are formed and improved solder flow over the gold surface occurs.
A Practical Guide to Achieving Lead-Free Electronics Assembly
Abstract. To successfully achieve lead-free electronics assembly, each participant in the manufacturing process, from purchasing to engineering to maintenance to Quality/Inspection, must have a solid understanding of the changes required of them. This pertains to considerations regarding design, components, PWBs, solder alloys, fluxe s, printing, reflow, wave soldering, rework, cleaning, equipment wear & tear and inspection.
Reflow Profiling: Time Above Liquidus
Abstract. Despite much research and discussion on the subject of reflow profiling, many questions and a good deal of confusion still exist. What is clear is that the pains often associated with profiling can be reduced if there is a strong understanding of the variables that can be encountered during the reflow process, as well as the metallurgical dynamics of the soldering process. This paper shall provide a brief outline of the reflow profile in general, with specific emphasis placed upon the suggested time spent above the melting temperature of the solder. The guidelines for soldering to various surfaces and with alternative solder alloys also are discussed.
A Comparison of Leading Lead-Free Alloys
Based on recent market developments, it appears that the choice of suitable lead-free alloys to replace Tin-Lead for electronics assembly is narrowing. Three candidates have emerged as potential standards for the industry. They are the Tin-Copper eutectic (Sn 99.3, Cu .7), the Tin-Silver eutectic (Sn96.5, Ag3.5), and CASTIN (Cu .8, Sb .5, Ag2.5, Sn96.2). In order to make objective comparisons between the three alloys, extensive testing covering several variables was conducted.
Unsure which Solder Alloy is most suitable for your application? Download our guide for an overview of some of the most common Solder Alloys and the technical specifications. For further advice, specific to your application, contact our Technical Sales Team.