Reading time ( words)
Material jetting processes are very similar to the above. Resin is loaded into a printer, where it travels into a printhead, the printhead has several nozzles or resin dispensers (much like a two-dimensional inkjet printer). The resin is then extruded from the miniaturized nozzles onto a build platform in the two-dimensional cross section of the part. After, the layer is passed over with a UV light source or other light activation that cures the resin that was deposited. The printhead then deposits another layer on the previously cured layer, this is done repeatedly until the part is completed.
There are several materials that are available for 3D printing for various engineering uses. Various vendors offer over hundreds of different materials that are either specific to an application or to a specific desired characteristic. For this study, eight materials that are regularly used for engineering applications were evaluated and characterized to determine which can be used in PCB processes. Material identifying characteristic as well as the designation is shown in Table 1.
Table 1: List of materials evaluated for this study.
To properly characterize the materials that could be used for engineering applications, various tests were chosen and performed so that a decision tree could be created. The ultimate goal of the project is to be able to have a decision tree that can determine which material can be used for a specific application. The description as well as motivation to perform each test is below.
Thermal Mechanical Analysis
This test is performed to check the dimensional stability of a test specimen as well as calculate its Tg. The results of this test are important because they will indicate how the 3D printed specimen maintains its dimensional stability. For materials to be used in PCBA processes, all auxiliary components must retain their mass as well as dimensional accuracy.
Thermal Gravimetric Analysis
Thermal gravimetric analysis is performed to determine the temperature when the material, in this case, the test specimen, has lost 5% of its weight. For this study, the temperature used was 300°C. The results taken from this test help indicate the lifespan of a material, the faster it loses its weight, its lifespan decreases.
Thermal Life Cycle Test
For this test, the 3D printed test specimens were subjected to 200 cycles of a predetermined temperature profile. Each cycle was the same in duration of time. The results of this test show what happens to a 3D printed test specimen when subjected to high temperatures. Any indication of warpage, delamination, degradation or other visible and/or cosmetic damage is important to capture. The results from this test indicate which materials are suited for high temperature applications in the PCBA process.
This test is a calculation based on the various parameters of a test specimen. The density was checked after thermal and chemical resistance testing. The results of this test are used to determine how well the test specimen can hold its mass after being subjected to either chemical or thermal stresses. The density check of test specimens helps determine which application it is suited for.
Chemical Resistance Test
The chemical resistance test is performed by subjecting the material to various chemicals. The test specimens are submerged in a chemical solution for a given period and then are subjected to a drying cycle for a given period. This test is important in the material characterization process due to it being an indicator of how the materials will react in various chemical exposure applications.
Electrostatic discharge check is a very crucial test in the characterization process since this determines whether the 3D printed material can be used with or around live PCBs or any other components that carry a charge. The values obtained with the ESD check for each of the materials assist in the ranking of the materials for application use.
To read the full version of this article, which appeared in the April 2018 issue of SMT007 Magazine, click here.