Programmable Strain Gage Amplifier Installation Notes

Amplifier Module Installation - Soldering Procedures

Intro

The RAETECH SG Amplifier was designed to provide a previously unavailable level of functionality in the smallest package possible. Like the strain gages with which it is used, good soldering technique is vital to avoiding damage and achieving a quality result.

Iron & tip

You will want to use a temperature-controlled soldering station with a chisel tip. An unregulated iron, or that thing that your dad gave you with the dual headlights that looks like a '50s sci-fi movie ray gun, are like using an axe when you need a scalpel. A chisel tip allows for quicker heat transfer to the joint than pointed tips. We use a 1.5mm chisel tip for our installations. Set the temperature of the iron to accommodate the solder that you are using.

Solder & flux

Your application will dictate what solder you will need to use. As a point of reference, the solder we usually use is .031" diameter, 97% tin, 3% copper with a flux core and a melting point of 572°F (300°C). Alternatively, a .025", 60% tin, 40% lead, flux core solder will provide easier workability due to its lower melting temperature (376°F/191°C) and near-instantaneous flash from liquid to solid thereby preventing "cold" solder joints. Applications where lead is permissible, however, are becoming increasingly rare. A liquid rosin flux is also very useful (even with flux-core solder) to assist solder flow-out and minimize the time the iron is in contact with the joint. It is vitally important that the flux is thoroughly cleaned from the completed joint. Cleaning agents that have been used successfully with the RAETECH SG Amplifier include toluene/isopropanol rosin solvent, commercially available spray electrical contact cleaner or automotive spray brake cleaner. It is the end-user's responsibility to determine if these solvents can be used safely in their installation.

Wire gauge

We use 34ga. to 24ga. wire in our installations. If your application requires the use of a larger diameter wire, we recommend that you transition to 34ga.-24ga. wire via a bondable terminal strip. Large diameter wire joints require increased heat to flow out the solder, increasing the possibility of damage to the solder tabs. Additionally, soldering wires larger than 24ga. to the amplifier increases the chance of "bridging" multiple tabs.

Amplifier bonding

The SG Amplifier is potted in high temperature epoxy allowing a wide variety of adhesive options depending on the requirements of your installation. Simply remove the serial number label and wipe with solvent to remove any residual label adhesive and mold release.

Soldering

Tin the tip: Coat the tip thoroughly in molten solder. For best results, keep a blob of molten solder on the tip whenever it is resting in the stand.

Tin the tab: Lay solder over the tab, clean the tip, pick up a small bead of solder on the iron, touch the tip to the solder then lift away the iron and the solder simultaneously. The time that the iron is in contact with the tab should not exceed one second.

Tin the wire: Clean the tip, pick up a small bead of solder on the iron, hold it to the wire end and move the pair into contact with the solder.

Solder the joint: Brush a bit of rosin flux onto the solder tab. Clean the tip, pick up a small bead of solder on the iron and hold it to the tinned wire end. Touch the wire end and iron to the solder tab. Again, the time that the iron is in contact with the tab should not exceed one second.

Finishing

Clean: Remove the flux with solvent. Apply with a soft-bristle brush or low-lint swab. Remove solvent/flux mixture by wicking with the edge of a paper towel or gauze. Repeat until all flux is removed and then do it again just to be sure.

Inspect: A properly soldered joint will appear smooth, shiny and uniform. Check for any residual flux (Magnification is helpful). Any questionable joints should be re-fluxed and reheated. Be sure to hold the wire in position and limit contact with the iron to one second. Then, clean, clean, clean.

Seal: The base layer sealant that we use is a high-solids, acrylic coating. It provides non-corrosive protection from subsequent coatings yet leaves a solvent-soluble layer between delicate solder joints and, perhaps, more aggressive sealants. Subsequent coatings are application dependant. Most commonly we use Dow Corning® 3145RTV or an application appropriate epoxy.

Support: Whatever coating you use, it is vital to make sure that the area where the wires transition from the surface up to the solder tabs is filled to provide support.

Download as PDF: RAETECH Strain Gage Amplifier Soldering Procedures