Hot Air Pencils
Many of you, dear readers, will be familiar with hot air stations and their associated hot air hand-pieces.
They work on a very simple principle. Air pressure is created by a diaphragm pump, fan or turbine. The air is pushed past a heating element before exiting the hand piece barrel and being directed to the work piece via a suitable nozzle. There are many different nozzle types to suit different tasks. These include BGA rework and differing sizes of SMT components down to the smallest parts.
Air flow and temperature is controllable by the user to suit the components being heated. Too much air flow can literally blow components off of the PCB. The temperature is set, just as with a soldering iron, to that suitable for the size of component and its heat absorption capability.
Now that we have got the basics out of the way, what is a hot air pencil ?
The name describes this tool well but some are larger and fatter than others so less 'pencil' like ! The operating principle is the same as a conventional large hot air station and hand-piece. The difference comes in the precision nature of the hot air pencil when compared to its bigger 'generalist' brothers.
A hot air pencil receives pressurised air from a station that usually contains a piston or diaphragm pump. The pump has to cope with small hose and nozzle diameters without problems. The pressurised air usually passes through the pencil hand-piece and into a heating element barrel that looks similar to that of a soldering iron. It is thin but, importantly, hollow so that air can pass down its centre. In the end of the heater barrel there is a very small diameter air nozzle from which the heated air emerges.
The diameter of the hot air nozzle and its associated hot air jet is the advantage that the hot air pencil has over its bigger brothers. Nozzles of 1.2mm internal diameter are common. It is not normally possible to use such small diameter nozzles on conventional large hot air station hand-pieces as the heater can suffer low air flow over heating and failure.
Why use a hot air pencil with such a small hot air jet diameter?
Modern SMT PCB's can be densely populated with the smaller sizes of SMT components such as 0603 and 0402. These components are positioned so closely together that great care is needed when carrying out soldering or rework on the PCB. Some equipment contains IC's that are known to be very sensitive to overheating and you do not want to blast them with hot air if you can avoid it.
The hot air pencil is a precision tool whereas the conventional and larger hot air hand-piece is a somewhat more blunt tool, with less precision and control over the hot air stream confinement.
I 'made do' with my general-use hot air station when working on SMT PCB's for some time. I stumbled upon a hot air pencil on eBay and took a chance on it. As soon as I started using it I realised just how useful such a precision tool really is. I have not looked back since. I still use conventional hot air stations but where I need to have greater control over what is, and is not, heated, I always reach for a hot air pencil. I have worked on 0402 SMT resistors and capacitors with ease thanks to the finely focused air jet and adjustable air flow. When working on high density 0402 PCB's I have found the hot air pencil truly invaluable. It also performs well on many other sizes of SMT components and even multi pin SMT IC's. With a hot air pencil you can even rework individual pins on an IC without reflowing the whole IC in the process. You do need to consider thermal differential across the IC wen doing so however as some IC's do not like this reflow approach.
Does a hot air pencil have limitations when compared to a conventional hot air hand-piece ?
Absolutely ! The hot air pencil produces a very fine jet of hot air and, as with a soldering iron tip, you need the appropriate size end piece for the task. The hot air pencil is brilliant on small SMT components but it cannot cope with long multi pin connectors, large SMT components such as power inductors and larger multi-pin IC's.
Large components tend to absorb the heat more quickly and the fine air jet has to be moved back and forth along multi pin parts rather than the broader hot air stream from conventional hot air pieces that heats many pins at once.
Would I recommend adding a hot air pencil to your workbench ?
If you already have the larger type of hot air hand-piece, yes. The hot air pencil cannot replace a conventional larger hot air hand-piece, but it is a valuable addition to the tool arsenal. Just like a fine soldering iron for 'micro-soldering'.
Which are the best brands of hot air pencil ?
This is a difficult question as hot air pencils are not as common as conventional hot air hand-pieces and so there is less choice. Just as with soldering irons, the selection process is very much personal choice. Be it hand-piece design or affordability. Hot air pencils do tend to be expensive, both new or used.
I own several hot air pencils that I have bought over the years. As with most tools, you get what you pay for and cheaper units are likely to be less ergonomic or less well constructed. I have the following types:
1. OKI SHP-1060A
2. R.E.L HAP (Hot Air Pencil)
3. PACE Thermojet
4. Xytronic HAP80
My personal favourite is the OKI-1060A and I own three of them.
The hot air pencils do need a station to power them and provide air. The OKI and R.E.L. hand-pieces use dedicated stations. The PACE and Xytronic hand-pieces attach to standard de-soldering stations that also provide an air output. Most hot air pencils can be fitted with different diameter and shape tips to suit the task at hand. I use straight and bent tips in my OKI-1060A's.
The cheapest hand-piece is the Xytronic HAP80 at £28 +VAT from Rapid Electronics. You do need the 8800 desoldering station to power it though !
I have not tested the Xytronic HAP80 yet as it arrived today. I have no reason to believe it will not work as advertised however. the hot air tip design is not just a hollow tube. It has side air entry ports to increase the heat uptake of the air passing down the barrel and through it.
I am including some pictures of my hot air pencil hand-pieces and a pile of components that I removed from a scrap PCB with the OKI-1060A in just a few minutes. It is just so easy and controllable to use .
Fraser
First pictures are of the OKI hand-pieces....