Solder Heat Resistance Test

     

Solder Heat Resistance Test (SHRT), as the name implies, is a reliability test for assessing the ability of a device to withstand the thermal stresses of the soldering process.  It is also sometimes referred to as 'preconditioning' if it precedes another reliability test. 

                             

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Preconditioning is usually done for surface-mount devices prior to PCT, THB, and HAST, all of which accelerate corrosion if the package cracks after preconditioning.  Preconditioning may also be done prior to temperature cycling or thermal shock, both of which aggravate incipient mechanical failures induced by the precondition.  In effect, preconditioning simulates the board soldering process while the tests following it simulates the stresses that the device will experience after mounting.

   

Solder Heat Resistance Testing consists of three steps:  1) a bake to drive away all the moisture within the samples; 2) a temperature/humidity soak to drive controlled amounts of moisture into the package; and 3) a form of thermal shock simulating the soldering process itself.  

  

Popcorn cracking, which is package cracking resulting from internal vapor pressure from within the package during soldering, is the primary failure mechanism accelerated by SHRT.  If the package delaminates internally during SHRT, neck breaking and ball lifting may also be accelerated.  Die cracking may also result from SHRT.  Lastly, because SHRT involves a step that promotes moisture ingress into the package, moisture-related failure mechanisms may also arise after SHRT, but these should generally not be considered as valid SHRT failures.

  

Baking is usually done for 24 hours at 125 deg C or 8 hours at 150 deg C.  Soaking is usually done at 85 deg C/85% RH or 30 deg C/60%RH, for a duration ranging from 24 hours to 192 hours, depending on the moisture sensitivity of the package.

                       

The thermal shock may be provided by a vapor cloud, infrared (IR) heating, convection heating, or a combination of IR and convection heating.  The profile of the thermal shock consists of a temperature ramp of about 2-4 degrees per second to a peak temperature of 220-260 deg C.  The shock is often done three times, and should be completed within 4 hours after the soak.  Visual inspection and electrical testing are the tests for success or failure after SHRT.   

                

    

Fig. 1. Example of an IR Reflow Oven; note the long conveyor belt

that transports the samples through the required temperature profile

   

 

Reliability Tests:   Autoclave Test or PCTTemperature Cycling; Thermal Shock; THB HAST HTOL LTOL HTS; SHRT Other Reliability Tests

  

See Also:  Reliability Engineering Reliability Modeling;

Qualification Process; Failure Analysis Package FailuresDie Failures

 

   

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