IPC/JEDEC standards applicable to connectorsHigher lead-free SMT soldering temperatures will force changes from currently used connector housing resins which will melt, suffer pin retention failures, or fail to meet dimensional stability requirements. Adopting established and accepted IPC/JEDEC standards on handling requirements, moisture absorption control, and blister prevention enables the use of non-LCP resins for lead-free SMT assembly. Because connector manufacturers lose control of their connectors once they are sold, it is important to educate the entire connector value-chain to implement these JEDEC-based handling/packaging requirements. Moisture absorption is one of the main causes of blistering in connector housing.
Blistering of IC packages, called “popcorning,” during surface-mount assembly,
has resulted in industry-standard packaging based on the IC package
performance after environmental conditioning. This component performance is
measured as a Moisture Sensitivity Level (MSL) and is defined in the standard
shown below. Moisture/Reflow Sensitivity Classification for Nonhermetic Solid State Surface Mount DevicesThe standard is based upon several conditions including relative humidity and uses a lead-free reflow profile that results in a 250°C temperature (+0/-5°C) on the package topside surface in an eight-minute maximum (25°C to peak temperature) profile. Peak oven temperatures of more than 300°C are typical in order to generate this 250°C surface temperature.
 IPC/JEDEC J-STD-033B Handling, Packing, Shipping, and Use of Moisture/Reflow-Sensitive Surface-Mount DevicesBased on the results of the testing in various conditions and this reflow profile, standard requirements are given to ensure the protection of these devices in this follow-up industry standard. The PC board assembly industry has incorporated these handling guidelines for the IC packages in order to avoid the cost penalty of board re-work if “popcorning” occurs.
 Qualification Procedure for Lead-free ConnectorsA connector industry consortium developed a heat resistance qualification procedure to determine the suitability of connectors for lead-free solder processes. This procedure incorporates the conditioning and soak requirements from IPC/JEDEC J-STD-020C for determining Moisture Sensitivity Levels (MSL) as part of the testing protocols. The MSL used in the qualification test is IPC/JEDEC Level 1 which has a moisture soak requirement of 168 hours @ 85°C/85% RH. There are 2 reflow profiles used in the testing and the peak reflow temperature is measured at the top of the connector. The first profile has a peak temperature of 245°C, which reflects the temperature control capability of small PCB assembly. The 2nd peak reflow temperature is 260°C. These temperatures reflect the » 15°C higher reflow temperatures required with lead-free solders Failure criteria are as follows:
Failure tolerance is zero connectors out of 5. No connector housing resins consistently pass (no blisters + dimensional integrity maintained) lead-free solder profiles of 260°C at the IPC/JEDEC MSL Level 1 soak requirements. Even some liquid crystal polymers (LCPs) exhibit occasional blistering at solder temperatures (both conventional and Pb-free) due to degradation that occurs in molding or from trapped gasses. Blistering on an LCP mPGA Socket Housing
 During SMT assembly, connectors are exposed to high oven temperatures required for solder reflow. This results in a super-saturated condition in the parts where the moisture creates substantial pressure against the sidewalls thereby creating a “blister”. The majority of non-LCP connectors that meet lead-free SMT assembly process conditions fall into the IPC/JEDEC J-STD-020B MSL levels of 2 – 5a and will not pass the connector consortium qualification procedure as it is currently written. Many current high-temperature resins will pass lead-free solder surface mount assembly if care is taken to keep moisture absorption below the threshold level where blister onset occurs. This can be done using moisture barrier packaging or adopting solder pre-drying procedures. |
