clamping aids

Solder wire is an alloy which mostly consists of tin (Sn) and caontains some smaller quantities of silver (Ag) and/or copper (Cu). Other metals are possible but less common. In the lab we only use lead-free solder (Pb free). Lead-free soler wire usually has a melting temperature of 217-227°C. Solder wire usually also contains flux inside. For most soldering operations extra flux will not be necessary. Some hints:

• Do not tear off solder wire from the spool as you will not have flux at the points of separation. Use a cutting tool or use a soldering iron to cut of pieces of solder wire.
• Do not curl up solderwire in your hands. Skin fat and oil can hinder soldering.
• Choose the right solder wire diameter for your task. In the lab you may find 0.35mm, 0.7mm and 1mm wire.
• Solder wire likes to be stored dry an cool. It may have an expiration date (important for industry), it will also work years after that time.

The purpose of flux is to remove the oxidised layer on the PCB and the component directly before the soldering process. Usually there is a sufficient amount of flux in the solder wire (or paste). In some occasions it is needed to add extra flux to improve soldering. For example hen repairing or when the soldering process is taking too long. The flux pens you will find in the lab are of the “No-Clean”-type, which means it can stay on the PCB after soldering and does not need to be cleaned. Using flux gel is sometimes help as it will stay in place after dispensing it. Most soldering fluxes come in liquid form.

• Use only as much flux as needed.
• Use REL0 or ROL0 types preferrably as they are least aggressive and are mostly free of halogen.

As stated above the flux available in the lab can stay on the PCB. In case you want or need to clean your PCB from flux residues complete the following steps:

• Wet the affected areas with isopropyl alcohol.
• Scrub the area carefully with a suitable (ESD) brush.
• Rinse the PCB by tilting it. Remove residues with fuzz-free (ESD) rag (pink). Residues should not go under neighboring components on the PCB.
• Dry Let it dry by air. Do not use compressed air as it may cause ESD issues. Slowly drying flux may be removed with the fuzz-free rag (pink: ESD). Test: a clean surface will not feel sticky.

In order to tin cable ends you can use a solder bath.

• Wear sfatey glasses.
• Turn it on and wait until the solder melts.
• Remove the oxidised first layer with the spatula.
• Use a cable stripper to prepare your cables.
• Dip the cables in flux.
• Dip the cables in the solder bath. Stop 1 mm before the insulation of the cable.
• Let the bath cool down and clean up the workspace.

There are two options available to dispense solder paste on a PCB at the university:

• Stencil printing (only possible if you have a stencil for your PCB)
• Individual dispensing using a hand dispenser which employs compressed air

Please note that there are different pastes for each of the two options due to the different viscosities needed.

The lab is currently not a proper ESD environment. It is possible to destroy components due to electrostatic discharges. However you can take some precautions to reduce the risk of ESD.

• The grey mats on the workplace are ESD protected
• Leave the components in the bag when moving in the lab.
• Use an ESD wristband whenever working with ESD sensitive components.