Rick Littlefield, K1BQT 109A McDaniel Shore Drive
Barrington, New Hampshire 03825
e-mail: <[email protected] Quarterly Devices
The DEN-ON SC-7000Z Vacuum Desoldering Tool

Few designers or low-volume repair technicians can afford the luxury of a full-blown SMD rework station. Instead, most of us improvise with what we've got, while keeping an eye open for new low-cost tools to make the job easier. For example, to solder, I use a combination iron and vacuum-sucker soldering station liberated from a flea market at a fraction of its as-new price.

This works OK, but what I really want is an all-in-one gizmo that can wire-solder, air re-flow, extricate SMD parts, and free tight leads from stubborn plate-throughs. I'd also like to get rid of the compressor, air tank, hoses, tangled cords, and shoe-box sized vacuum unit presently cluttering up my lab.

Description

The DEN-ON SC7000Z is a handheld desoldering device with a built-in suction pump and filter. It performs the same basic function as a much-larger bench-mounted vacuum system. However, there are several differences and added features that make the SC-7000Z ESD safe for C-MOS devices. The unit's vacuum pump, flow valve, and filter are located in the body, and pump's drive motor is inside the handle. This may sound like a hefty handful of hardware, but the entire package barely weighs a pound. Operation is totally silent, except for pump noise when the trigger is depressed.

Compared to a bench-top vacuum unit powered by compressed air, the SC-7000Z not only saves space, but also a considerable amount of money. To illustrate how much money, the current list price for my bench-top station is over $1,100, plus another $250 for a small compressed-air setup with all the required hoses and attachments. The SC-7000Z, on the other hand, sells for $395.00 (current sale price with stand). If this were simply a powered vacuum-sucker alone, you'd already be $1,000 ahead of the game. But its more.

Unlike my fixed-temperature bench-top station, the DEN-ON unit is temperature-adjustable from 350 to 500 degrees Celsius (662 to 932 degrees Fahrenheit). This means you can set the tip temperature to accommodate a wide variety of components and PC boards. Heat is generated by a barrel-mounted, 100-watt ceramic element. This unified design minimizes conduction distance to the tip, and temperature is held constant by a sensor-feedback control circuit. A thermostat LED indicator remains lit during warm-up and blinks when the unit is at temperature. Warm-up from a cold start takes about two minutes.

Perhaps the most significant feature of the SC-7000Z is its ability to reverse air-flow and function as a positive pressure hot-blow system. This adds the capability to air-desolder LSI chips and other SMD parts. It also allows you to use re-flow pastes for installing parts with pin spacing too close to wire-solder with an iron. To change modes from powered suction to hot-blow soldering, you'll need to change tips, substitute a bypass cartridge for the unit's suction filter, flick the air-direction lever, and turn up the heat. This procedure is simpler than it sounds and takes less than a minute to complete.

In comparing the SC-7000Z to a bench unit, I should note that most vacuum stations are designed to run all day--every day--in a high volume production environment where compressed air is readily available. Most of them also provide a high-quality temperature-controlled soldering iron as part of the package (something the SC-7000Z does not). The SC-7000Z, on the other hand, is designed for intermittent use in a low-volume shop, field-service, or lab environment. Here, small size and versatility are especially valued features. It's simply a matter of choosing the right tool for the job; for many of us, a production-line vacuum station is overkill.

Manufacturer's specifications and claims are always interesting to read, but using a product for real-world tasks is more telling. When I set the product literature aside and applied power the SC-7000Z, I wondered how a small handheld-unit could seriously compete with an industrial-grade vacuum sucker. About two minutes later, the thermostat LED started to blink and it was time to find out.

To provide a true acid test, I pulled a rejected radio transceiver board from my junk box. Unlike most digital boards, this particular RF layout harbored a host of nasty-to-remove through-hole parts stuffed into large heat absorbing ground-plane areas---a nightmare for most removal systems. For openers, I took aim on a 10-mm shielded RF transformer and pulled the trigger. The SC-7000Z's vacuum pump kicked in with a muffled "brrupp". As soon as I desoldered the last pin, the 10mm shield literally fell out of the board! I tried several more parts, and each one came out with equal ease. Through a combination of solid thermal capacity, stiff temperature control, and strong suction, the SC-7000Z lived up to its claims. It's a real performer!

The "gun" technique for removing parts is simple---just make sure the tip is well tinned and the plate-through is completely heated before you pull the trigger. Thorough heating ensures complete evacuation of the hole and pad area. One note of caution; the manual advises against suctioning up clipped wire leads. This can result in an unscheduled stop for a tip cleaning.

The spec sheet states that the SC-7000Z can clear plate-throughs on multi-layer boards up to eight layers deep, and even 12 layers deep when supplemental heat is applied to the bottom of the board. I believe it---the unit's internal pump develops over 650mmHg of vacuum in a mere 1/10 of a second! In fact, this is the only low or moderately priced system I've seen that has enough suction and thermal recovery to reliably clear plate-throughs implanted in large land areas.

Encouraged by the unit's performance on through-mount boards, I switched over to hot-blow mode. As long as you have a safe way to handle and cool the extracted tip, you can switch modes while the unit is still hot. To use the hot-blow mode effectively, however, you'll need to purchase the accessory SMD Tool Kit ($42). This package includes a special elongated tip that delivers superior air heating, a baffled bypass cartridge to replace the fiber-filled suction filter, and a SMD removal tool with a collection of stainless-steel wires and blades for lifting various SMD packages.

After setting up for hot-blow operation, I located a scrap board containing an SMD IC with 0.05-inch pin spacing. To ensure sufficient air temperature, I set the thermostat for 450° C (more tip heat is required for hot-blow procedures than for suction removal). To remove the IC, I installed a thin stainless-steel wire in the SMD removal tool and slipped it behind the IC pins on one side. After preheating the pad area for a couple seconds, I began to pop each lead off its pad with the SMD tool, moving down the length of the chip while continuing to apply heat. This procedure worked exactly as advertised, and the chip came out cleanly without damage to the board.

Next, I extracted a few 1206 resistors, heating each one with a jet of hot air and plucking it off the board with tweezers. The SMD tool may also be used for removing discrete parts such as capacitors, resistors, and inductors. Simply substitute a small blade in place of the wire. Finally, to push the envelope, I reinstalled the same IC I had removed, using solder paste and a construction aid to hold the chip in place. This was a slightly more challenging task, but, once again, the gun's air temperature was more than adequate to heat the pads quickly and re-flow the paste.

As with any vacuum desoldering system, the SC-7000Z requires periodic maintenance. However, thanks to some forethought on the part of the manufacturer, I found this quick and easy to perform.

The pathway from tip to filter cartridge is short, straight, and very hot, so there's little opportunity for solder to ball up and become trapped in either the tip or suction line. To clear solid debris, the instructions suggest reversing the air-flow briefly prior to shutdown. A more thorough tip cleaning is accomplished with a cleaning pin (a set comes with the unit). For dissolving residual flux, the literature suggests occasionally removing the tip and soaking it overnight in acetone.

To protect the unit---and to protect your self from the hot tip---I strongly recommend ordering the SC-7000Z with the ST-800 stand. This heat-resistant holder not only allows safe storage when the unit is turned on, but also provides a cleaning sponge for keeping the tip bright and clean. Also, to prolong life, the instructions recommend tinning the tip occasionally with fresh solder and remembering to turn the unit's thermostat down to minimum heat during prolonged periods of inactivity.

The other important maintenance item on the SC-7000Z is the unit's filter. All vacuum systems require an in-line filter to prevent solder debris from being sucked into the pump. The disposable DEN-ON filter cartridge is made from shatter-proof high-temperature plastic, and it ejects easily from the top of the unit with the pull of a release lever. Routine cleaning is easy, and cartridge handling is far less touchy that with the high-temperature glass-tube filters used in many bench-top stations. A catch-plate (or baffle) in the DEN-ON cartridge prevents rapid fouling of the filter's fibrous material and prolongs the filters useful life. When the fibrous material finally becomes contaminated, replacement cartridges are available for about $4.00 each.

Overall, I found the SC-7000Z to be a first-class performer. For one thing, it did everything the promotional literature claimed it would. More importantly, however, it fulfilled several valuable functions I routinely need when proto-typing new designs for both through-lead and SMD style packaging. If you're looking for a low-cost way to add vacuum-powered suction and hot-blow capability to your bench, this unit is a hard act to beat!

The DEN-ON SC-7000Z is presently available from Howard Electronic Instruments, Inc. for sale price of $395.00. This price includes the ST-800 stand, a standard-profile 1.0mm ID suction tip, a spare filter, and a tip-cleaning tool ($375.00 without stand). Other standard and slim -profile tips are also available as accessories in 0.8 mm, 1.0 mm, and 1.5mm ID sizes, along with disposable replacement filter cartridges.

In addition to purchasing the basic unit and stand, I strongly suggest ordering the 72-78-00 SMD Tool Kit ($42). This accessory is essential if you wish to use the hot-blow feature of the unit for SMD work.

You may contact Howard Electronic Instruments, Inc. for literature and more information at 1-800-394-1984 and 1-316-321-2800 via voice, or at 1-316-321-2803 via Fax. The e-mail address is Contact Us. The regular mailing address is Howard Electronic Instruments, Inc., 974 SE Pioneer Rd., El Dorado, KS 67042. All units purchased carry a 60-day fully refundable money back guarantee, and a one-year warranty. The company also carries a line of DEN-ON premium-grade temperature-controlled soldering irons to compliment the SC-7000Z.