Don’t dispose of circuit boards when you can diagnose, rework, repair and keep using them!
by Luca Conte
The rework of circuit boards has increased drastically over recent years due to the shortage of components in the global market. Many technology users and service providers are quickly becoming aware of needing to repair and recycle their electronic equipment and components, not only for financial benefit but in order to reduce waste and its damaging effects on the environment.
Printed Circuit Boards Assemblies (PCBA) have evolved significantly within the last decade, seeing the introduction of tiny and fine-pitch components, and heavier thermal boards. In addition, new lead–free soldering alloys also add further complexity to the rework process. These recent changes make it even more crucial to have all the elements needed to perform perfect rework procedures and eliminate any risks to critical solder joints.
Firstly, considering the manual tools needed in rework is essential. Rework can be handled in a variety of different ways, depending on the component, operator’s skills and preferences, and tool availability. Very few applications require just a soldering iron with the appropriate tip. Classic tips such as “GW” tips are quite often used to suck-up short-circuits, chisel tips are used to desolder passives; and both are used to clean pads in a safer way than the ‘old school’ way of desoldering braid/wick.
In certain rework processes, such as desoldering a dual–line component, it is beneficial to use a tool such as desoldering thermal tweezers – like Weller’s WXMT and WMRT. The tweezers simultaneously heat both sides of the component, allowing for fast and accurate desoldering of both small and medium dual-line parts. Weller’s tweezers and soldering heads are also available in Military Standard, broading the scope of industry in which these innovative products can be used.
For most operators, the quickest and most convenient way to desolder chips and other SMDs with leads on two sides is to add enough soldering alloy on the contact surface, to enhance heat transfer with all the parts involved.
Weller’s WMRT thermal micro tweezer
Alternatively, some may still have a preference for the use of hot air as a rework tool and so a small/medium size hot air pencil would be the choice, rather than a high power/air flow gun. Weller offers two different powers in this range; 100W on HAP1, for the older units, while 200W on HAP2 and WXHAP200. These small ergonomic pencils can blow up to 18lt/min (depending on the size of the model) of deionized air, at a maximum of 550°C. They can be equipped with a range of nozzles, starting from a round 0.8mm and up to a square 18x18mm. If connected with WXR3 or WR3M, Weller’s hot air pencils can be used with the WRK reflow kit: this desoldering set optimizes the process and enables chip components to be lifted precisely and without damage during desoldering. In the Weller range there are nozzles that can desolder components from 3×3 mm, up to 30×30 mm.
For 4–sided and “leadless” components, the only efficient answer is removal via hot air. Traditionally for such components, most certainly the larger ones, a high-power hot air gun is required. Weller’s portfolio of products provides 2 different solutions: WTHA1 and WHA3000. Both are digital and stand-alone units with a built-in pump, and the option of a venturi valve (in the WHA3000 only) for Nitrogen or compressed air.
Weller’s high power hot air guns
WTHA1 has 900W of power and can blow up to 100lt/min of hot air at a maximum of 600°C. It works by setting the temperature and flow, and simply pressing a switch to turn it on or off. There is also an option to set a thermal profile, consisting of temperature, airflow and even time for each phase. WHA3000P has an added vacuum feature; allowing the user to take the component off automatically after desoldering. The WHA3000P can also run a thermal profile of 3 steps, including the needed preheating temperature (as the preheating plate can be handily connected to the unit). This unit has the capability to connect a thermal sensor to study thermal profiles if required.
In many desoldering cases, preheating is highly recommended (even mandatory in some cases). If the user is unable to work at high temperatures of preheating for various reasons, even a low temperature (60/80°C) will ease the process. For those working at high temperatures Weller’s heating plates are a well known and recommended product, commended for their precision and reliability. They are adaptable to the user’s needs; the largest plates have the capacity to connect a thermal sensor as a “pilot of the system” (the temperature set on the plate will be the target point on the sensor), and control the amount of ceramic heaters being used, depending on the users needs.
WQB4000SOPS Semi automatic rework unit with “split optic”, for QFPs, QFNs and BGAs
Weller’s complete rework systems WHA3000PS and WQB4000SOPS are supplied with preheating plates for this exact reason. Set WHA3000P consists of a preheating plate and circuit + hot air gun holder, whereas set WQB4000SOPS is a semi-automatic rework system with “split optic positioning system”, a feature that enables the user to view the components’ alignment before soldering. With its precision, power, and easy-to-use 8 phase thermal profiler, WQB4000SOPS is consistently the first choice for the military sector and EMS.
PTH desoldering is also covered by Weller products, as the company launched new high-power desoldering iron available in three different versions. With their fast heat up time (around 35”), high power (120W), and innovative “long tailed” nozzles, Weller’s desoldering irons are the most efficient, precise, and safe products in the market. The long tailed nozzles allow good surface contact, and their shape ensures that soldering alloy is driven to the collector in hot conditions, without cooling down and potentially solidifying which can cause a multitude of problems. It is of vital importance to choose the correct nozzle to avoid such issues.
Weller WXDP120 high power ergonomic desoldering iron
An important part of desoldering is maintenance of the units and tools. In order to prevent damages to your equipment, you must follow your supplier’s maintenance instructions, which often include regularly checking tools and units’ filters. Good reworking is given by a good and fresh soldering alloy. It is often difficult to add fresh solder when perfoming electronic rework, as you should use an alloy that is compatible to the one employed in the assembly process. Working out the alloy could be an impossible or expensive task.
Weller offers both ROL0 and ROL1 liquid flux as a solution to this, to be used to prepare parts to be reworked, and also different types of leadfree soldering wires. All the wires are all No-clean alloys, characterized by the presence of micro additives that reduce oxidation and erosion of the tip, ensuring a constant presence of thefluxing core, to obtain repetitive and quality results. Greater fluidity, less splashing and the possibility of working at lower temperatures brings the operating costs back to optimal levels, with added benefits of greater productivity, better quality and longer life of the tips and components.
Weller offers a wide range of solder wires
Alongside flux and soldering alloy, it is beneficial for users to have a good filtration system, as during reworking the amount of fumes generated is usually more than in standard soldering applications. This is due to the parts involved potentially being dirty; coated with resins and glue, and additional flux being used in the process – reworking can potentially create dangerous substances that must be kept out of the breathing zone. Weller offers 2 types of 3 stage filtration systems: the “tip extractor” for extraction of fumes directly next to the soldering iron or air gun, or the “volume extractor” which covers a much bigger surface area compared to the previous, and old style, system. As with the maintenance of desoldering tools, it is important to check and maintain filtration systems to the highest standard as per suppliers instructions. The filters must be checked and replace filters regularly: at least once per year for the main filter, and more frequently for pre-filters – the units are designed to alert you when any filters need changing.