Navigating Capacitor Screening Standards

Posted by Bob Nelson on Aug 14, 2019 9:25:00 AM

Compared to other applications, a medical implant is a rather benign environment for a capacitor; it’s temperature-controlled with a relatively low voltage. That being said, the success of a capacitor in a medical implant relies heavily on manufacturing components to avoid failures and the know-how to screen for any production discrepancies. As the reliability grade of a component progresses, more screening and testing is required to ensure that only the most robust parts make it to the finished product.

MIL-55681 and MIL-123 are common standards for medical applications like implantables; MIL-55681 requires 100 hours with a looser Percentage of Defectives (PDA). MIL-123 requires 168 to 264 hours with a tighter PDA towards the end of the screening process for lot clear out.

For MIL-123, the allowable PDA is 3% overall and 0.1% in the last 48 hours for capacitance/voltage values listed in MIL-123, see Table 1. Beyond MIL-123, the requirement is 5% overall and 0.2% in the last 48 hours for the capacitance/voltage values. If unable to meet the strict criteria, the whole lot will be rejected. The processis complicated by the large quantity of parts required to move through screening and into production. With strict MIL requirements, manufacturers need the capacity to accommodate large lots.

Patient safety and quality of life are major concerns for medical device companies. While there are many related concerns that manufacturers cannot directly resolve, high quality and screening standards remove some of the uncertainty and lessen the possibility of failure in the field.

Knowles Precision Devices (KPD) High Rel products are designed, tested, and screened for optimum reliability to MIL standards, or customer SCD. Military performance specifications are designed and written for the voltage/capacitance ratings of the individual product slash numbers associated with the specification. With a customer tendency towards SCD based on MIL-55681, Knowles has a wealth of knowledge to help adapt and compile. Years of industry experience can help inform atypical SCD needs, too.

Specification

Description

Requirements

MIL-PRF-55681 (Group A)

General purpose military high reliability specification for surface mount sizes 0805 through 2225 in 50V and 100V.

  • VOLTAGE CONDITIONING
  • 100 HRS, 2X VDCW, 125°C
  • DWV, IR, 125°C IR, CAP, DF TEST
  • VISUAL & MECH. INSPECTION (AQL SAMPLE PLAN)
  • SOLDERABILITY, SAMPLE 13(0)
  • 8% PDA MAXIMUM

MIL-PRF-123 (Group A)

The specification affords an increased reliability level over MIL-PRF-55681 for space, missile and other high reliability applications such as medical implantable or life support equipment. The specification covers surface mount sizes 0805 through 2225 in 50V rating and various radial / axial leaded products in 50V, 100V and 200V ratings.
  • THERMAL SHOCK, 20 CYCLES
  • VOLTAGE CONDITIONING 168/264 HRS, 2X VDCW, 125°C
  • DWV, IR, 125°C IR, CAP, DF TEST • VISUAL & MECH. INSPECTION SAMPLE 20(0)
  • DPA(1)
  • • PDA, 3% (0.1%), 5% (0.2%) MAX(2)

Table 1: Strict military specifications to screen capacitors in life-critical applications.

While many manufacturers can accommodate MIL-level screening, KPD has performed to these standards for years with no field failures. KPD believes in designing robust components from the outset and maintains the ability to process about four million parts per month to uphold strict screening procedures.

KPD has provided capacitors to implantable device manufacturers for 25 years; in that time, none of its product have been involved in recalls. The screening and quality assurance efforts provided by KPD are guided by a long history of reliability. We refuse to compromise on quality or safety.

For further reading on the cost of device failures and how proper reliability testing and supplier considerations can help you navigate sourcing decisions, download our white paper, “The Price of Reliability: Considerations for Buyers.”


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Topics: Capacitor

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