RoadTest: Cool Tools: Desoldering Station - 110V
Evaluation Type: Workshop Tools
Did you receive all parts the manufacturer stated would be included in the package?: True
What other parts do you consider comparable to this product?: Aoyue 474A++, Hakko 32TU99
What were the biggest problems encountered?: The manual is not of very good quality, and is missing important use and care information.
The Tenma 21-19700 desoldering station is a quality tool, and a good value. It can’t do everything, but it excels at the tasks it can handle. The manual leaves a lot to be desired, and is probably the weakest part of the package.
The station arrived packed in a single plain brown carton. The carton wasn’t particularly heavy cardboard, was crushed at the corners, and was ripped at one corner. Sturdier cardboard would seem to be in order for the outer carton. The peripheral parts and accessories were packed in plastic bags inside the main carton, while the base unit was inside a plastic bag and surrounded by two additional molded cardboard trays. The manual was inside the carton as well.
The accessory pouch was nice to have, and includes a cleaning tool, a small hand drill for really tough cleaning jobs, a tube of silicone grease, and an assortment of spare parts: six filter sponges, one spring, one filter barrel cap, and two desoldering nozzles. Part numbers for the spares are not indicated in the manual, but some do appear listed at the bottom of the product page on newark.com.
The manual is not very good; it includes pictures of all the parts and some useful exploded-view diagrams, but it is decidedly lacking in important details. For example, the indicator light on the front is on constantly when the unit is heating up to the target temperature, then starts flashing when the unit achieves the target temperature. I know this because I observed the behavior of the unit while testing it, but this fact does not appear anywhere in the manual. There is no indication in the manual of what temperature ranges correspond to the numerical settings printed around the front-panel knob. The cleaning instructions are a helpful start, but they are incomplete. The instructions do not indicate what the user should do with the included silicone grease; I deduced eventually that it is best suited to application on the inside tip of the filter spring.
The construction of the unit seems sturdy. There is a screw on the bottom that must be removed prior to use (it secures the pump during shipping); this fact is mentioned in the manual, and again on a sticker that covers the IEC power cord inlet. The electrical cable and vacuum line running between the handpiece and the base unit are bundled together into a harness using small plastic clips. Both the vacuum tubing and the wire insulation are heat resistant, displaying no melting, warping, or discoloration after being touched with the heated tip of the desoldering tool.
TESTING - First set
Materials: Wire (14ga and 24ga stranded), 60/40 solder, FR4 scrap, 2-layer and 4-layer PCBs, various passive components
Conditions: The heating control on the front of the 21-19700 was set to ‘6.’ The tip attained a temperature of 400°F after heating for one minute.
Test 0: Remove installed parts from PCB
The station performed extremely well, removing five potentiometers having six pins each (two of which were kinked press-fit structural support pins) in about five minutes from switch-on to completion. For each pin, about five seconds of heat-up time were followed by two to three seconds of vacuum time. Kinked structural pins required two passes. The components released with only slight additional heating to the structural pins.
Test 1: Remove solder from ground plane
The station performed fairly well, removing most of the solder in three tries. About five seconds of heat-up time were followed by about three seconds of vacuum time during each try. The copper at the center of the soldered patch has wrinkled/torn some, suggesting that the copper is pulling away from the substrate.
Test 2: Remove solder from filled PCB through holes
The station performed well removing solder from filled holes in both the two-layer (green) and four-layer (blue) PCBs. About five seconds of heat-up time were followed by about five seconds of vacuum time, then the board was flipped and the process repeated.
Test 3: Remove soldered-in through hole components from PCBs
The station was able to release the 1/8W resistor from the four-layer PCB with an assist from some tweezers, but the large copper pours attached to the holes on the two-layer PCB proved to be too much for the station to handle. About five seconds of heat-up time were followed by about five seconds of vacuum time.
Test 4: Remove soldered-in through hole component from milled FR4 blank
The station was able to remove a 1/4W resistor from the milled blank without removing the very small traces from the substrate. About three seconds of heat-up time were followed by about two seconds of vacuum time. The component released with only slight additional heating to each leg.
Test 5: Remove SMD component from PCB
The station technically removed the 0603 resistor, but the resistor became lodged in the opening of the desoldering tool tip and had to be removed with tweezers. About two seconds of heat-up time were followed by about two seconds of vacuum time; this process was repeated twice on each side of the component. Removing small SMD parts is not a practical application for this tool.
Test 6: Remove wire leads soldered to PCBs
The station performed extremely well releasing 24ga wires soldered to both two-layer and four-layer PCBs. About three seconds of heat-up time were followed by about two seconds of vacuum time.
Test 7: Remove wire soldered to connector pin
The station performed extremely well removing a 24ga wire from the post of a JST 5-pin connector. About one second of heat-up time was followed by about one second of vacuum time. The plastic housing of the connector did not warp, melt, or discolor. The pin remains firmly affixed within the connector.
Test 8: Remove wire soldered directly to through hole LED leg
The station performed extremely well removing a 24ga wire from the leg of a yellow 5mm LED. About one second of heat-up time was followed by about one second of vacuum time. The plastic housing of the LED did not warp, melt, or discolor. The diode remains intact, and illuminates as expected.
Test 9: Remove cold solder joint from PCB/component interface
The station performed extremely well repairing a cold solder joint from the interface between a PCB and a 1/4W resistor. About two seconds of heat-up time were followed by about one second of vacuum time. In addition to removing the cold joint, the remaining solder flowed around the pad and component lead to form a much better joint.
Test 10: Disassemble two wires soldered together (24ga)
The station performed extremely well releasing two 24ga wires soldered to one another. About one second of heat-up time was followed by about two seconds of vacuum time.
Test 11: Disassemble two wires soldered together (14ga)
The station performed acceptably releasing two 14ga wires soldered to one another. About five seconds of heat-up time were followed by about three seconds of vacuum time. This process was repeated twice, once on the exposed end of each of the wires, removing the majority of the excess solder. Slight additional heating was required to release the wires from one another.
TESTING - Second set
Materials: 60/40 solder, 2-layer and 4-layer PCBs, various passive components
Conditions: The heating control on the front of the 21-19700 was set to ‘8.’ The tip attained a temperature of 460°F after heating for one and a half minutes.
Test 12: Remove soldered-in through hole components from PCBs
The station was able to release the 1/8W resistor from the four-layer PCB with an assist from some tweezers, but the large copper pours attached to the holes on the two-layer PCB were still difficult for the station to handle. The station was able to free one leg of the 1/8W resistor, but I had to resort to coaxing the other leg out by applying additional heat with a soldering iron. About five seconds of heat-up time were followed by about five seconds of vacuum time. This procedure was repeated twice on each leg for the four-layer PCB, and thrice on each leg for the two-layer PCB.
The 21-19700 desoldering station is fairly easy to use. The main pitfall awaiting the unprepared is the tendency of the tool to clog. Using proper technique helps immensely with this problem; you should continue to keep the trigger depressed for a second or so after you remove the tool from the work to ensure that all solder has been pulled into the chamber and none remains in the nozzle (Thanks to user mcb1 for the tip in the comments!) There is an indicator on the side of the handpiece that changes from blue to red (only when the trigger is depressed) that indicates a clogged tool. The provided cleaning pin works well to clean the nozzle, which should be done while the tool is hot. After the tool has cooled, it can be disassembled for further cleaning. The spring filter tends to clog; accumulated solder sometimes forms a mass inside the point of the spring, with a small protrusion sticking through to the other side. The easiest way to remove such a mass is to apply heat to the protrusion outside the tip of the spring with a soldering iron while the spring is upright on a heat-resistant surface; the rest of the mass will fall out of the spring. Once the inside tip of the spring filter is clear of solder, apply the included silicone grease to the inside of the spring tip using a q-tip or similar application tool.
The 21-19700 desoldering station is a simple tool the performs its function well at a reasonable price. It performs far better than similar tools I've used from well-known brands in the solder/rework tool space in some tasks, and though the manual does not give as much information or instruction as it should, the tool is simple enough that one can learn how to use it well fairly quickly.
The unit is extremely effective at capturing solder. The primary capture mechanism is the spring filter located behind the inlet nozzle, which catches >90% of the solder. The secondary mechanism…
You're keen desoldering smd with this tool, it's usually a hot air blower and tweezers.
The main pitfall awaiting the unprepared is the tendency of the tool to clog
I've seen this with…
I was curious how the unit captured the solder and how easy it was to clean the capture chamber?
Very thorough road test - well done.
The outer case is made of what appears to be powder-coated steel, and the panels are 0.043" thick including the coating. The top handle and all front and rear panel jacks, connectors, and switches are all firmly attached to the casing and operate as expected. The rubber feet are suitably large and prevent the unit from sliding on surface. All screws and fasteners are firmly attached. I would say that it is solidly built.
Most of the cleaning rods that I have seen for this type of desoldering station are made of stainless steel. The poor heat conductivity of stainless means that usually brute pressure must be applied to remove a clog. I have found that by using an appropriate 18 or 20 Ga copper wire I can transfer heat from the heater back to the clog and melt it away as well as push it. If you try this technique it is important to hold the wire with a pliers or needle nose as the heat quickly transfers to both ends of the wire.
I think you're on to something here. I have been using this tool in exactly the manner you describe, releasing the vacuum actuator switch when I remove the tool from the work area. I'll try running the vacuum for an additional second or so to see if that makes a difference in how often the tool needs to be de-clogged. I'll update the review accordingly if your proposed technique addresses the issue.
I've added photos of the handpiece fully disassembled, and with just the vacuum chamber and secondary filter removed. They are in the "USE NOTES" section of the review. The vacuum pump runs only when the trigger is actuated. The base unit generated about 80dB SPL (unweighted) measured at 1m when the vacuum pump was operating.