AN607

Rev. 1.7

11

4. Humidity and Temperature Sensor Special Handling Considerations

4.1. Product Storage

The Si70xx are shipped in sealed anti-static bags. The sensors may be stored in a humidity and temperature

controlled (RH: 20% to 60%, Temp 10 °C to 35 °C) environment for up to one year after being removed from the

bag prior to assembly (the moisture sensitivity rating is MSL2). Do not store the humidity sensors in polyethylene

bags (typically blue, yellow, or pink) because these emit gases that can affect the sensor. Metallic, anti-static,

sealable, moisture-barrier bags are recommended for storage. Do not use sealants or tapes to seal inside the

packaging.

4.2. Use of Conformal Coating and Under-Fill Materials

Use of conformal coating or under-fill material is possible with the following cautions:

sensing layer of the Si70xx as they will adhere to the polyimide film and cause a permanent shift in the

humidity sensor readings. Even very small particles can have a significant effect.

Following are general recommendations to avoid humidity sensor drift from fumes:



Cover the Si70xx during the application process with a cover that forms a seal on the device such as Kapton™

KPPD-1/8 polyimide tape.



The optional Silicon Laboratories protective cover will not block fumes, but it will block liquids and particles. It may

be effective if the fume concentration is not high.



Use low volatile organic compound (VOC) materials.



Immediately cure the material in a well-ventilated environment.

We recommend that a test run be performed to measure humidity in a controlled chamber before and after the

coating process to make sure no shifts are occurring. If a humidity-controlled test chamber is not available, perform

a side-by-side test with one board coated and one board not coated. These cautions are consistent with all

polyimide-based relative humidity sensors. In general, if a process has been qualified with a similar part from a

different vendor, it will be acceptable for the Si70xx devices.

4.3. Assembly Flow

Limit soldering iron rework to five seconds per lead, for compete rework use a new sensor as manual removal and

soldering can shift senor accuracy outside of data sheet limits. Avoid the use of hot air rework tools.

Figure 8. Limit Solder Rework to Five Seconds or Less

The humidity sensor opening should generally be covered during soldering to prevent flux from getting on the

sensor surface. Further it is recommended that the Si70xx only be soldered with standard reflow (no hand

soldering or hot air tools). The hydrophobic filter is compatible with standard reflow soldering. If the hydrophobic

filter cover is not used, Kapton tape will serve the same purpose, although it has to be removed after soldering.

Soldering iron touch-up is possible if liquid flux is not needed and care is taken to avoid excessive heating (five

seconds per lead). If complete rework is needed, the recommended method is to use a new part and reflow the

entire board.

 

 

 

 

 

 

 

5 seconds 

maximum