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Product category: PCB Assembly Equipment and Tools
News Release from: Metcal | Subject: SmartHeat
Edited by the Electronicstalk Editorial Team on 11 December 2001

The hidden costs of hand soldering

Today's electronics manufacturing and rework place tight demands on the humble soldering iron.

Dating back to the early 1920s, standard soldering irons have been around longer than PCBs themselves Although there have been improvements in the shape, ergonomics, output, heating efficiency and temperature regulation of the standard soldering iron, the science has remained, in principal, just as it was 80 years ago

For most industries, the standard iron is a good choice for small repair work.

However, the same cannot be said for electronics manufacturing.

The staggering evolution of processes and automated machinery, coupled with reductions in board and component size and increased board density have been accomplished by equipment and process enhancements.

Yet, when it comes to using a soldering iron for the rework and repair of increasingly expensive PCBs, little has changed.

Modern rework requirements, driven by demands for smaller, faster and cheaper products have created the need for innovative materials and tools - including newly designed soldering systems.

Densely populated, multilayer boards and miniaturised, high-pin-count, fine-pitch devices cannot be efficiently repaired using the technology of past generations.

Yet throughout electronics manufacturing, technicians are forced to struggle with soldering irons that offer little process control, forcing them to make almost random decisions about tip temperature, which, in turn, often results in damaged components and scrapped boards.

Eutectic solder melts at 183C.

The basic rule of thumb when using a soldering iron is that it's best to use the minimum temperature possible when repairing or reworking, allowing reflow in a reasonable time but posing minimum threat of damage to the component/PCB.

Older soldering irons work on the "fixed power, variable tip temperature" principle.

As the phrase implies, power remains constant whilst the operator, using a dial on the soldering unit, adjusts tip temperature.

However, fixed power is often too much for a light solder joint and not enough for a heavy one.

Because technicians can and often do change temperature settings from day to day, job to job, solder results can be inconsistent.

To further complicate matters, the irons must be constantly recalibrated to ensure that, for example, a 200C tip is indeed reaching and not exceeding that temperature.

While standard soldering irons ue constant power and variable temperature, one newer system recognises the damage this unpredictable process can have on sensitive components and substrates.

Termed 'SmartHeat', this 'next generation' soldering technology has turned traditional repair and rework on its head, moving the dependence of joint quality away from operator skill, onto the inherent technology of a soldering system that employs variable power at a fixed temperature.

SmartHeat allows for conduction at minimum controlled temperatures.

With this technology, the metallurgical qualities of the tip determine the temperature.

Because the tip regulates the temperature (to an accuracy +/-1.2C), the operator cannot adjust it, thus total process control, repeatability and consistency are inbuilt and nonadjustable.

Variable power, fixed temperature technology solves several problems posed by today's assemblies.

Damage to components/PCBs is virtually eliminated because the ideal tip temperature is never exceeded.

Operators are not required to make critical decisions about the application of thermal energy.

The ergonomic design of SmartHeat irons and tips allows operators to solder/desolder and rework smaller components with precision and without needing to constantly recalibrate.

This means that operators require minimal training to be able to use the iron and they achieve greater productivity through not needing to continually wait for their iron to reheat between jobs.

It is a misconception that all soldering irons perform the same function with equal speed and quality.

It is also untrue that the cost-effectiveness of an iron is based purely on its up-front cost.

It's understandable that, particularly in lean times, saving money on equipment expenditure is an intelligent way to control costs.

However, it is poor business sense to make savings on an initial purchase knowing that with an advanced soldering system such a price difference will be swiftly recovered and exceeded through increased profitability.

As PCBs become increasingly sophisticated and valuable, soldering systems must be able to solder and resolder components with speed and safety.

If not, scrap rate increases whilst profitability decreases.

Yet, many in the industry continue to overlook the value of proper repair and rework, and do so, by equipping their operators with older tools that regularly damage assemblies.

It is ironic that when a PCB arrives at the rework department it is worth more than at any other stage of the assembly process, yet it is often greeted by a standard soldering iron that offers no process control.

A quick, high quality repair means the board can be sold and will not end up as expensive scrap.

A poor repair job means the entire cost of manufacturing the PCB is lost.

Granted, through initial cost comparison, a next generation soldering system may appear a luxury option reserved for high-end rather than mainstream manufacturing purposes, but in today's competitive marketplace, all PCBs are high-end and all are costly to scrap.

Real cost-effectiveness can only be judged by considering all the costs - the up-front price of the system plus the cost of running it.

Productivity rates, potential downtime (due to recalibration and maintenance), operator training and damaged assembly costs must therefore all be taken into consideration.

As consumers have learned, avoiding low-cost less-efficient alternatives and purchasing a quality, functional product as an initial investment subsequently saves time and reaps money.

For electronics manufacturers, savings made through using the correct soldering tool are both qualitative, in terms of reduced scrap and greater throughput, as well as quantitative, reducing thermal stress to assemblies, increasing uptime and raising productivity.

The key criteria for selecting any soldering system are the protection of components, the reduction in the need for tip replacement, the avoidance of increased power consumption, the speed and quality of the repair and the elimination of the downtime recalibration requires.

With a standard soldering iron, its real price is evident once the repair process has been completed - or the board has been turned to scrap.

By automatically adjusting its own thermal power output, SmartHeat hand soldering systems adapt to suit the thermal load of a component.

The capacity to automatically adjust power feeds a constant temperature to the solder tip, protecting sensitive components whilst meeting the thermal capacities of larger ones.

The fact that it's the soldering system and not the operator that adjusts the operating temperature means that there is no need to stop the rework process for re-calibration.

Throughput is increased, damage to components and PCBs is virtually eliminated and downtime is reduced.

A notable cost saving with SmartHeat irons is evident when temperature adaptability is measured against the thermal inertia caused when using standard hand soldering options.

After recalibration, operators must wait for the iron to reach its optimum working temperature.

When this delay is added to the time taken for recalibration itself and the length of time the operator is unable to work, recalibration becomes an expensive hidden cost of hand soldering.

The amount of labour involved in the soldering process directly affects the value of each PCB.

Adding hidden rework expenses to the cost of manufacture clearly demonstrates the extent to which a nonefficient hand soldering system can affect bottom-line profitability.

If recalibration of standard irons is neglected, inaccurate heating levels and increased likelihood of scrap are the results.

Controlling the iron tip temperature is not the only issue to be considered.

The critical element is regulating the heat cycle of the work.

How fast the solder joint reflows, how quickly it reaches the optimum reflow temperature and how long the joint stays hot are critical to reliable connections.

Older soldering irons find it difficult to reach optimum temperature and to remain there.

Subsequently, operators are often required to add thermal energy; increasing risk of damage.

With inbuilt thermal stability, SmartHeat irons can undertake even the most demanding of task, regulating their own tip temperature to within 1.1C of a setpoint, ensuring faster soldering at a lower temperature with no operator adjustment.

This last point is critical.

With a high turnover of rework staff, it is often difficult to find an operator with the experience necessary to ensure a consistent level of throughput and quality.

An inexperienced operator may not have the necessary skill to adjust tip temperature or to recalibrate standard irons.

Such an uncertainty is removed if you redirect the thermal responsibility to the next generation soldering iron, guaranteeing that even the most unskilled of operators can perform their jobs well with minimum training.

Faulty solder joints remain one of the major causes of equipment failure, and thus the importance of high-standard soldering workmanship cannot be overemphasised.

In relation to repair and rework, the main cause of solder joint defect is poor wetting.

This is a preventable danger caused by an over-heated solder tip burning away the flux before it can do its job.

This causes an increase in soldering time and hampers joint formation, by preventing solder from sticking to the iron's working surface.

When a solder tip doesn't reach the required temperature, the cause is usually the build-up of oxide acting as a thermal insulator, thus impairing heat transfer.

When using standard irons, operators will often boost the power input in an attempt to increase tip temperature.

The elevated thermal demands placed on the tip to perform quickly add to overall processing costs, as tip life is greatly reduced.

The need to continually replace tips drives up the cost of hand soldering.

With SmartHeat, an acceptable tip life can be achieved, in part because the technology uses the lowest temperature necessary to reflow the solder joint.

Reduced temperatures and tip stress can extend tip life and lower the overall cost or repair and rework.

In fact, with a SmartHeat iron heat is not 'stored' in the soldering iron tip, but applied directly from the heater to the joint.

If the tip cools while transferring heat to a joint, for instance, the tip cartridge instantly responds by safely increasing power to restore tip temperature.

With lead-free processes, which reflow at temperatures as much as 40C above eutectic solder, tip life on standard irons is even further reduced.

SmartHeat's ability to solder at lower temperatures will offer greater advantages, as lead-free soldering becomes mainstream.

Lead-free also presents other challenges - the most critical being the soldering of heat-sensitive boards and components at the greatly increased 215-220C melting range of lead-free alloys without causing damage.

This consideration is made particularly pertinent by the fact that most components are specified to a maximum temperature exposure of 240-250C.

With such a tight (20-30C) margin for error, operators need to employ soldering irons that offer fixed temperature control.

Irons that cannot will almost certainly cause thermal damage to components and delamination or scorching of substrates.

One final advantage of adopting variable power, fixed temperature soldering is its versatility.

It is frustrating, especially in the fast-paced, high turnover world of electronics manufacturing to have to wait for an iron to recalibrate or to switch between systems separately designed for soldering, desoldering, repair or rework.

With a single SmartHeat system, an operator can switch seamlessly between such tasks as well as between applications as diverse as 0201s and ground-planes.

With the power and flexibility to adapt to a range of processes, any extra initial costs are swiftly recouped through the elimination of downtime, calibration and thermal inertia achieved with this advanced hand soldering technology.

SmartHeat variable-power fixed-temperature soldering irons come into their own for all hand soldering, desoldering, repair and rework tasks once you evaluate the true costs of all soldering irons.

They are also the only real option when conducting lead-free rework and repair tasks.

While they may be more expensive out of the box, SmartHeat irons prove their economic sense when considering the increase in productivity they provide, the ongoing costs of iron maintenance and recalibration, and the reduction in component/PCB scrap.

Modern electronics manufacturers need to reassess line productivity as a whole system in order to increase throughput.

This necessitates considering end of line innovation alongside technological advancements in capital equipment.

With PCBs becoming more densely populated and components increasingly expensive, rework and repair has never been so important or made such a difference to throughput quality and yield.

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