Moisture can be trapped inside plastic-body surface mount components after prolonged exposure of the components to a** IS IT NECESSARILY HIGH HUMIDITY ENVIRONMENTS high-humidity environment. ** THE HIGH TEMPERATURES High temperatures applied to the components during reflow can cause the moisture inside the component to vaporize. The expansion of the vapor pressure inside the component often creates minute cracks and/or delamination of critical interfaces within the package. The burst of vapor pressure can cause solder** THE SOLDER JOINTS to open and often results in an intermittent problem that is hard to detect ** OR COMPLETE FAILURE OF THE PART.
The future use of lead-free solder will further aggravate the moisture absorption problem because the reflow temperature will need to be increased by about 15°C to 20°C above the reflow temperature of the solder in use today. The management of MSD will be crucial to the successful implementation of lead-free PCB assembly.
Many resources on the Internet provide information on the specification and handling of MSD. For example, The SMTA Moisture Sensitive Devices (MSD) Council provides valuable information regarding the impact of moisture on the surface-mounted component. The IPC/JEDEC document, IPC/JEDEC J-STD-033A July 2002 sets forth "standardized methods for handling, packaging, shipping, and use of moisture/reflow sensitive SMD packages" which have been classified to the levels defined in IPC/JEDEC J-STD-020B.
The specifications list the length of exposure to moisture for different MSDs after the MSD is removed from the moisture barrier bag. The humidity level and temperature during the exposure affects whether the part is safe to use or needs to be baked at approximately 125°C to remove the moisture. Successful MSD management should have an accurate way to monitor the actual time that the MSD is exposed to a particular relative humidity level at a certain temperature so that the MSD 1) is not subject to un-necessary baking, and 2) receives an acceptable level of moisture exposure to endure the reflow process.
To date, a number of techniques have been used to ensure that the moisture exposure level is within the specifications. Unfortunately, these techniques require numerous steps and manual labor in handling the parts. The most common way of keeping track of MSDs is to attach a label ** ANY WAY TO ACTUALLY SHOW A TYPICAL LABEL. ANYONE WHO TRIES TO UNDERSTAND THE INSTRUCTIONS FOR THE FIRST TIME WILL BE SHOCKED onto the reel or tray of MSDs and manually record the time when the MSD is removed from the moisture barrier bag and the time when the MSD is put into or removed from the dry box. ** THEN THEY HAVE TO DO THE CALCULATIONS BEFOR RELEASING THE PARTS .
** NEW PARA Alternatively, a barcode or RFID is attached onto the reel or tray of MSD when the MSDs is removed from the moisture barrier bag. The barcode label is scanned or timing information is written to the RFID when the MSD is put into or removed from the dry box. In general, an action is required each time the MSD's moisture environment changes so that the data can be written either to a piece of paper, a central database, or an RFID. These extra actions add more workload for the operator and may require the use of another piece of software on the factory floor. More significantly, the accuracy of this type of system relies on the operator remembering to write or scan the information.** PLUS NO CONSIDERATION IS GIVEN TO THE DIFFERENT RHS THE PART MAY EXPERIENCE,
The HumiTel™ product is a simple humidity data logger specifically designed for MSD management. The user simply attaches the HumiTel™ ** PICTURE NEEDED; to the reel or trays of MSDs when the MSD is removed from the incoming moisture barrier bag. The HumiTel™ records the ambient relative humidity and temperature at a preset time interval, thereby providing a full history of the MSD's moisture exposure. Prior to placing the part onto the printed circuit, the moisture exposure history of the MSD is read and the MSD PASS/FAIL is then determined by a specification such as the JDEC JTD-033A. If a customer ** CUSTOMER OR CUSTOM? specification is desired, the PASS/FAIL can be re-adjusted to the new specification.
The HumiTel™ ** HUMITEL DEVICE consists of ** 3 MAIN PARTS, a humidity sensor, an EEPROM, and a battery which supplies power to the module. The module can record 4 data points per hour for approximately one year. The duration of the battery depends on the data rate (number of samples per hour). The HumiTel™ module is enclosed in a small ESD-safe enclosure.