At this point in our process we have a produced the exact alloy that you have requested. But, a large piece of solder isn’t going to help you assemble microelectronics components. We need to start manipulating the solder into a usable form; in this case a preform.
NEXT STEP: The freshly-alloyed solder is extruded to convert it from a stout chunk of metal into a long, thick ribbon. This ribbon won’t be what you need either (assuming you need a preform) but, it is a step in the right direction. Just as with alloying, there is a science to extruding different solder alloys. The Indium Corporation has been perfecting this for over 80 years.
In general, extrusion is a process of pushing metal through an opening in the end of a chamber. The chamber opening forms the material as it exits, and the material will retain a cross section that resembles the shape of the opening. With ribbon, a rectangular opening is used. Maybe you had a Play-Doh extruder as a child, or perhaps your child has one – this is very similar to the process we are discussing with solder, only with much less pressure). This is also a very good method for making wire.
THEN: After the solder is extruded, it is ready for rolling. Rolling takes place between two large cylinders. Maybe you have seen those machines that flatten a penny and emboss something into the surface at tourist destinations? This is similar to what we are doing with our rolls – except our rolls are much larger and flat (and we don’t have to crank them by hand!). We use the rolling mill to flatten the extruded ribbon down to the thickness of the preform.
The next step to make a preform is cutting the parts out of the ribbon we just created.
*This post is part of the World of Solder Preforms series
Window screen frame extrusion image courtesy of atozscreens.com.