Hey team,
I had a customer reach out about the HDC2010 and are having issues with some failures in fabrication (ie shorts, rotations, flux build-up blocking the sensor element).
Some additional background:
"We created our PCB footprint based on the datasheet recommendations, but our CM came back with EQ’s recommending we change the pad size from the recommended 0.263mm to 0.345mm due to concerns with solder wetting on the lead-free HASL finish PCB’s we were using. They also gave us the option to change to OSP finish. Not knowing the trade-offs of the different finishes we ended up changing the pad size. In hind-sight, it isn’t too surprising that we had a fairly high percentage of failures on the soldering"
They were looking for the following information:
"Does TI have any recommendations as far as soldering of this part? Is there a recommended board finish? Special solder that wets better? Re-flow temperature profile? Etc., etc.? I do not know the pros/cons of the different board finishes and I don’t want to blindly switch to the OSP finish our CM recommended and have it fix the issue with this component but cause problems with other components."
Some information I found via silicon guide:
The sense layer must not have direct contact with cleaning agents such as PCB board wash after soldering. Applying cleaning agents to the sense layer may lead to drift of the RH output or even complete breakdown of the sensor. Avoid strong blasts from aerosol dusters and use only low pressure oil free air dusting.
The HDC must be added in the last assembly step. In case the PCB passes through multiple solder cycles (as is the case for PCBs that have components on the top and bottom side), adding the HDC last reduces the risk of damage to the sensing polymer from contaminants or excessive heat.
It is important that no-clean solder paste is used and no board wash is applied once the sensor is assembled onto the PCB. To ensure proper device performance, these instructions should be communicated to board manufacturers before assembly.
Some info from the datasheet:
10.1.1.2 Soldering Reflow
For PCB assembly, standard reflow soldering ovens may be used. The HDC2010 uses the standard soldering profile IPC/JEDEC J-STD-020 with peak temperatures at 260°C. When soldering the HDC2010, it is mandatory to use no-clean solder paste, and the paste must not be exposed to water or solvent rinses during assembly because these contaminants may affect sensor accuracy. After reflow, it is expected that the sensor will generally output a shift in relative humidity, which will reduce over time as the sensor is exposed to typical indoor ambient conditions. These conditions include 30-40% RH at room temperature during a duration of several days. Following this re-hydration procedure allows the polymer to correctly settle after reflow and return to the calibrated RH accuracy.
10.1.1.3 Rework
TI recommends to limit the HDC2010 to a single IR reflow with no rework, but a second reflow may be possible if the following guidelines are met: • The no-clean solder paste is used and the process is not exposed to any liquids, such as water or solvents. • The Peak soldering temperature does not exceed 260°C.
Is there any other information we can provide? Thanks!
