Please note that the following refers to FR4 as the pre-processed substrate produced by Cartesian Co. The current revision of FR4 is a sand blasting surface treated sheet measuring roughly 150x100mm with a thickness of 1.5mm.
FR4 is a glass reinforced epoxy laminate that is often used in standard PCB production. The material is extremely stiff, strong, durable & available for cheap from many sources due to its prevalence in the PCB industry. The sand blasted surface of FR4 provides an ideal surface for high resolution, high conductivity prints. FR4 can also be soldered to quite easily & does not stain from the Nitric Acid chemical byproduct of the ink reaction. Unfortunately, the smooth surface of stock FR4 sheeting does not provide a surface conducive to bonding the Silver traces & it must be pre-processed before printing onto.
Where to Find
Pre-processed panels of sanded FR4 will be able to be purchased from the Cartesian Co Web Store shortly. Sheets of FR4 with or without Copper cladding can also be found from various suppliers online - if you're lucky you may also be able to find a local supplier of good quality FR4 that is used in the construction industry (although often the quality can be inferior). Note that in order to achieve high resolution & conductivity, the surface must be sanded to a very even & fine finish.
Coming soon: details of pre-processing steps to take stock FR4 to a state ideal for printing with the Argentum.
|5/5 The conductivity of FR4 is extremely favourable due to the fact that it has been sand blasted to an ideal roughness before shipping. This means the surface doesn't have any matrix weaving that the Silver tracks fall into (eg. Canvas Paper) & a continuous conducting path is built up & filled in very quickly.|
|5/5 For very similar reasons as the conductivity being beneficial, the resolution achieved on FR4 can be very high. The resolution on FR4 seems to be limited only by the cartridge resolution and the viscosity of the ink. It is easy to print footprints for 0603 components & if you tune your printer correctly & keep your cartridges in good condition, it is possible to create footprints as fine as TSSOP (0.635mm or 0.025inch pitch spacing).|
|4/5 FR4 does not appear to suffer the same reduction in adhesion that Kapton does during solder re-flow. With some practice, FR4 can be soldered to very easily but at first try, it is possible to pull up the Silver traces as the solder re-flows by using too high of a temperature. FR4 is however ideal for use on a re-flow hot plate, heat gun re-flow soldering as well as hand soldering.|
|4/5 FR4 is an extremely strong composite material that was originally developed as a fire retardant housing (hence FR4). Circuits produced on FR4 have been shown to be operational more than a year after printing. The only method that seems to cause the Silver to come up from FR4 is very high temperatures while soldering, scratching the surface of the prints actually helps apply high local pressure & 'actively increases conductivity' whilst making the tracks look extra nice and shiny silver.|
|0/5 FR4 is not flexible, it is a very stiff & sturdy material.|
|1/5 The greatest downside to using FR4 is that it is difficult to cut & shape. FR4 can not be cut using any reasonably sized CO2 laser system. Generally a power tool is required to make a clean cut & when doing so users 'MUST BE EXTREMELY CAREFUL OF THE PARTICLE DUST' as inhaling it is very harmful. Experiments are currently being conducted on thinner sheets of FR4 that can be cut with hand scissors but they are much more prone to de-lamination during soldering from heat.|