A paradigm shift is urgently required within the global electronic production industry to address the unacceptable equipment and methods commonplace for rework and repair of PCB's. While the response to the challenge presented by Surface Mount Devices (SMD) has been admirable with regards to high volume production, it has been lackluster and wrong in the realm work at the bench.

It is evident since the introduction of surface mount devices into printed circuit board (PCB) production some fifteen years ago* that both the methods and equipment used during rework and/or repair did not meet the challenges that Surface Mounting Technology presented at the bench.

* SMT developed in 1960's. Commercially viable in 1980's.

Webster's definition of "paradigm" is a standard method, pattern or archetype. This definition can be expanded by adding the words "generally accepted method or pattern". The definition of a "paradigm shift" is a change in a generally accepted method or pattern that produces a better or more efficient method or pattern for accomplishing the same result than as when using the former paradigm.

The old paradigm of using hand tools with elevated and damaging temperature ranges typical for decades with Through Hole Technology (THT) and traditional soldering irons unfortunately was carried over into the SMT rework lexicon. With few exceptions, the great majority of the manufacturers of soldering and desoldering equipment crudely attempted to repackage their existing THT products into some form of relevancy to SMD repair."

The decade long experience of SMD rework has yielded more than enough ample evidence to reject a paradigm that excuses lifted pads and traces, substrate delamination, warping, measling or bubbling along with discoloration of boards, thermal stresses and shock to ceramic chips, and most ominous of all: unseen thermal degradation of the integrated circuits (IC's) themselves.

Changing the Bench Paradigm: While most of these problems for the most part were rare in production work, they seemed to become the sad state of affairs within the rework discipline. It is time to change the paradigm.  During the last ten years market leaders within benchtop soldering and rework equipment industry failed to respond to the new SMT challenges. They chose to stay rooted within their comfortable, but increasingly irrelevant paradigm only making incremental changes to their existing products if forced to.

Worse, they never addressed the root problems within their old paradigm: unacceptable thermal excesses in their products. The consequence? The overall quality of rework and repair which had reached a very high standard with THT worldwide up to the mid-eighties hit what many now feel is perhaps the lowest quality level in the history of electronics. The blame belongs squarely with these benchtop rework equipment manufacturers.

The 20th century was a technological chronicle of innovation and obsolescence. It is very ironic indeed that the most innovative industry of them all, electronics, would have one sector so stubbornly rooted in the past, that being the rework and repair discipline.

With the use of traditional soldering irons on thru-hole components, it is important to point out that their high temperatures at the iron's tips were only  briefly applied selectively and directly to the chip's leads one at a time. With thru-hole technology, this was perfectly acceptable for many reasons: ceramic chips were rare, component density was rare, boards were populated only on one side; and the thermal application was to a single lead/pad interface at a time whether soldering or desoldering.

These new SMD's were on both sides of densely populated PCB's.  This made the former paradigm of high temperature contact impractical and damaging. The coming of the PLCC or J-Leaded devices made contact soldering next to impossible. Further removing any SMD required reflowing all leads simultaneously. Newer fine pitch and ultra fine pitch chips' leads were easily bent and damaged by pressure from soldering irons.

Some Bad Examples of SMD Solutions: Soldering station manufacturers' stubbornly stuck with with their old high temp approach.

They introduced goofy contact "SMD tips"  to "fit" onto their soldering irons. There were "SMD tips" for all SMD sizes. As the number of SMD's  increased, so did the number of "tips." This was simply dreadful: a.) solder on the lands did not reflow evenly; b.) excessive, inconsistent hand pressure damaged leads and pads; c.) and these tools were simply too hot (750°F to 400°C) for delicate SMD's. Further, the need for special "tips" for each SMD type became a PCB tech's nightmare and a costly program to maintain. Only soldering station manufacturers benefited.

The Hand Held Hot Air Jet With Nozzles: The next response by soldering station companies was perhaps worst of all. In the mid-1980's hot air hand jets were introduced into the rework market. These tools attempted to "focus" a stream of very high temp air onto non-preheated PCB's. The hot air was "focused" by nozzles, to reflow a chip's leads simultaneously. Marketed under different brands, these hand tools were called "hot air jets".  These hand tools caused terrible quality problems because they were used without preheat.

Why? Those marketing these tools did not manufacture preheaters. Worse, these companies were shamelessly recommending applications of extreme temps of 450ºC (750°F) to 500ºC (842°F) for soldering SMD's! But unlike soldering iron "SMD tips", these hot air jet indiscriminately propelled vary hot air gusts over not only a targeted chip, but also the PCB and adjacent chips. Thousands of PCB's were ruined by these tools during that era. Making these tools even more impractical was the continued march by designers to densely pack chips next to chips with each new generation of PCB layouts.

This is the present state of SMD rework equipment in the industry today. The engineers and technicians that are required to use this equipment and techniques have become very frustrated. The boards they are working with are more expensive and the cost of a damaged board has become a valid concern. No one wants to damage a board during rework, but unfortunately the rework tools currently available make that outcome more likely than should be.

Benchtop rework tools should duplicate the thermal conditions found in reflow ovens. The PCBA must be ramped up at 2-4°C per second and preheated to a temperature of 300°F for a period of up to 1 minute; as with reflow ovens. Jacks pointed out the many benefits of following that example, "Preheating the assembly activates the flux, removes extraneous volatiles from the flux, brings the metals to be soldered up to solder wetting temperatures, and elevates the temperature of the assembly in order to prevent thermal shock during exposure to the molten solder." And this cleansing from the activation of the flux just prior to reflow enhances the wetting process.

1.4 Preheating is Essential. Jacks taught "Preheating of the board at a lower temperature will prevent thermal shock, eliminating the fracturing which may otherwise result from the higher heat required to remove the target component.”

Different components on a board expand at different rates when high heat is applied. The resulting thermal discrepancies within the assembly create thermo-mechanical stresses which can and can cause embrittling, fracturing and cracking of those materials of lower thermal expansion rates such as chip capacitors and resistors. See the technical paper “Two Critical Benchtop Processes: Preheating and Post-Cooling.”

The World's First AirBath™ convective bottom-side pre-heater made the theory of preheating during rework into reality. Where hot plates failed, the air bath succeeded. There were no longer any excuses not pre-heating PCB's prior to rework.

With the AirBath™, the preheating revolution began and the paradigm shifted, but there was still yet one more amazing contribution to the PCB benchtop: Using low temp solder alloy to remove the SMD.

1.5 Using Low Temp Alloys for DeSoldering. Removing electronic components through the introduction of a targeted application of low temperature melting solder alloys had first been heralded and successfully proven practical as early as in the 1970's. Joseph Funari and William C. Ward are the most notable early proponents of the concept. Essentially, they proved that PCB devices could be de-soldered through metallurgy rather than high heat as in the past. Metallurgy is the science of mixing different metals together and can be used to remove any SMD from any assembly.

See How to Desolder Chips at 150°c

Biggest Change to the Soldering Bench in Decades: And at long last, at the 1996 Surface Mount International Exposition in Silicon Valley, the synergistic combination of convective bottom pre-heating (air bath) coupled together with a targeted application of low temperature melting solder alloy was first demonstrated to the world resulting in an instant recognition by industry leaders of the relevance to the discipline of rework and repair.

Industry Recognition & Praise: Indeed, the patented AirBath™ product and concept from Zephyrtronics was chosen as "The Best New Product" of the year winning the prestigious Vision Award for its innovative contribution to Surface Mount Technology.

Word quickly spread about this amazing synergy of forced-convection bottom-side preheating with low temperature solder alloys.

Four Methods of Preheat

Convective bottom-side PCB preheat together with low temp melting solder was a major "paradigm shift" for SMD removal and replacement. Quality temperature profiles are easily achieved by duplicating the original production thermal profiles during SMD rework. And what little time the entire removal and replacement process takes!

Still, the time saved must not be the only calculation for quality rework. Low temp profiles are also a must. IF one is truly calculating costs, then time, labor and material are components. But also one must weigh the unseen costs of damaged PCB's and chips (scrap) from excessive temps, and more importantly, the reliability and longevity of the reworked board once it is put back in service.

At the 1997 NEPCON West Expo, David Jacks challenged the entire industry with his milestone technical presentation in the official proceedings:  "The time has long passed for toleration of the double standard where PCBA production requirements are, on one hand, exacting while, on the other hand, those related to rework are lax.

The time proven thermal profiles that were the industry standard for production within the electronics industry for last half of the 20th Century must finally be brought to bear in the realm of rework and repair. The ending of the "Great Double Standard" requires only one thing: that manufacturing and quality engineers around the globe insist that the high temperatures long associated with rework become a relic of the past."

(Note: Jacks and Walston were later ceremoniously recognized and awarded by the electronics industry for their truly historic and milestone contributions to the global printed circuit board theater at the San Jose Convention Center in the heart of Silicon Valley. None other than the late, great Charles Hutchins himself accepted their award on their behalf.)

Quality Requires Change: In the past, rework was an afterthought. Today, lowering rework temps and eliminating hand pressure to chips are requirements for PCB work.

In the future, PCB's will be smaller, denser, expensive, and rework will continue. And so, safer, more reliable methods must be used.

After decades of bad SMD contact "tools" that relied on hand pressure, technique and thermally overloading, non-discriminating applications of hot temp air gusts to PCB's, a new paradigm has emerged that is sensible, practical, easy to understand, implement and brings all the positive elements of high volume PCBA production to the soldering bench. The lowest temp rework solution turned out as the easiest and most cost effective of all. The paradigm shifted.

About the Author: John Dwinell, Sr. was the long-time president of both Premium Parts Plus and the Projector Recorder Belt Corporation. A graduate of UW Wisconsin with a BS in Science, John also served with distinction in the United States Marine Corps as a 1st Lieutenant during in the Vietnam War. In the early 1980's John started a national distributorship of electronic chips and developed the first comprehensive cross-reference for replacement parts servicing the electronic entertainment industry. John is a regular speaker to the electronic community.