Choosing your next soldering tool
For most makers, hobbyists and engineers the soldering tool of choice is the trusty soldering iron, but the answer to the question of what tool next is not always obvious. Further still many find the task of reworking surface mount devices daunting and do not know where to start.
The right tool for the job
As with any task however, using the right tool for the job makes it a cinch. Searching for SMD rework will give hits for specialist tools and conflicting advice; for example, tools like BGA rework stations you probably don’t need (or can’t afford). Just like with a soldering iron there are good and bad practices, although there is no right or wrong answer, so everyone has an opinion.
This article is no different and something that works for us may not work for everyone. As with the old idiom, “there is no substitute for experience”, the best thing is having experience yourself followed closely by learning from others experience.
We recently needed to rework some QFP’s (Quad Flat Pack) and without a dedicated rework station it is a total nightmare. Yes it’s possible but only by stressing the PCB and IC’s well beyond there rated specifications and wrecking the removed IC in the process. Not to mention if a QA engineer sees you doing this they’ll have a heart attack!
Example reflow profile credit By Zithan (Own work) [Public domain], via Wikimedia Commons
All IC’s have a recommended reflow profile this is usually available from the datasheet of the FTDI 4232H. Straying beyond this is risky and can result in damage to the IC. At one end of the scale this can be cosmetic or result in performance degradation, at the other end the IC will literally be toast.
Using the FTDI 4232H as an example (the QFP we must rework) the maximum temperature the IC should get to is around 260ᵒC, and taking the IC much above this can damage the package and die. There are also specified ramp rates, both up and down. While these profiles are designed for production using reflow ovens with a much tighter control over temperature. When reworking it’s advisable to stick as close to these as possible by ramping up slowly and using as little heat as possible and allowing the cooling process to be slow.
Hot air rework
From our experience the right tool for this job is a hot air station and a good one is as versatile as the trusty soldering iron. There are many devices on the market some are better than others. Like soldering irons, prices range from very cheap to thousands. At most we will use the rework station a couple of times a week so we went with a budget RS Pro (124-4133)
Auto stop start
The unit came with everything needed to get set-up and running including the IEC power cable and we were soldering in minutes. The rework station pleasantly surprised us with the features it offers: this station comes with auto sleep, when removed from it’s holder the hot air starts and within a few seconds it will be up-to temperature; placing the device back on the station turns off the heating elements but the air stays on until the element/thermocouple temperature reaches around 100c to protect the station from damage. Having previously been using a 10 year old system the sound level was amazingly low in comparison. This device is far more suitable than the last station we used where disturbing others is an issue.
As can be seen in the video, changing the broken QFP went without a hitch and now we have a hot air station for other uses. These stations can be versatile and used with SMD parts from resistor/caps to BGA’s (again don’t tell your QA engineer, but it is doable for development purposes).
If you are not sold already, another example of the versatility of hot air rework was fixing some non cosmetic 3D prints (made from PLA) that had not adhered fully. Using the hot air to gently heat the print and re-adhere the layers went without a hitch. We must point out this is not a recommended it did result in ugly but salvaged our de-laminated prints.
One last point for any hot air station, be wary of where the nozzle is pointing when at rest. This hot air station needs to be at least 30cm from anything behind it or things may get a little scorched be wary of placement of the unit. i.e. don’t point it at your nice oscilloscope. The same goes for hot air operation the nozzle and air coming out are by the nature of the equipment very hot. It will turn plastic and solder molten very quickly, be cautious when using the equipment keeping your fingers out of the way and remember to read the safety parts of the manual to avoid some nasty burns.
What a lot of hot air