SOLDERING HIGH VOLTAGE MULTILAYER CERAMIC CAPACITORS
Multilayer Ceramic Capacitors (MLCC’s) are complex composite mechanical structures composed of alternating layers of a dense ceramic substrate and metal electrodes, which are connected by a metal termination that typically contains a glass frit. Each of these materials is characterized by a different Coefficient of Thermal Expansion (CTE), which makes the completed structure highly susceptible to thermal shock.
The degree to which a ceramic capacitor may potentially be effected by thermal shock can be influenced by several factors including the overall mass, size, and geometry of the device itself, the number, thickness and density of it’s ceramic layers and metal electrodes, the type of termination material utilized and the integrity with which these materials effectively form a single monolythic structure. In addition, there are several external influences that can also impact the degree to which a capacitor may be subjected to thermal stress including, but not limited to, the range of temperatures encountered, the means by which the part is exposed and time of exposure, the type of substrate to which the capacitor is being mounted, and the thermal characteristics and proximity of other components within the assembly.
While thermal shock conditions exist, the possibility of introducing substantial stress within the structure is significantly increased and unless preventative measures are introduced that mitigate these conditions, formation of micro fractures within the capacitor body are highly likely. These micro fractures, depending on their severity, may or may not be detectable thru common testing and inspection practices. This poses significant concern inasmuch as the suspect part may represent a latent failure whereby the product initially presents itself as an acceptable unit and may continue to operate until such time as moisture penetrates the flaw site, and / or it is subjected to further
mechanical of thermal stress. In addition, the actual failure may be delayed for an extended period of time and may not be detected until the finished product has been placed in the field.
 |
| MLCC Soldering at CalRamic Technologies LLC |
One area where the initiation of thermal shock can be addressed is in the soldering processes utilized for mounting ceramic capacitors. Ensuring adequate pre-heat and post heat conditions and the selection of the most appropriate soldering process can be critical to the success of the operation. This Application Note outlines some of the more common soldering processes utilized for mounting larger MLCC chip capacitors, including Infrared / Convection Reflow soldering, Vapor Phase Reflow soldering and Hand soldering. These recommendations if applied properly and tailored to the specific application, should minimize the risk for thermal shock and subsequent micro fracturing of these style capacitors.
