Connector Contact Retention

A key problem with wire harness assemblies constructed with crimp & poke style terminations is contact retention or terminal 'push back.' Many connectors in use today utilize crimp-on, removable contacts for termination.

    tpa-clip-sm            milspec-220            mate-n-lock-c

The Effects of Contact Retention Failures

 

Contacts inserted into the correct cavity that 'push back' or come loose at a later time can cause:

blu grydot  Electrical Open circuits

grey square  High Resistance Connections

grey square  Intermittent Connections


The problem is that un-seated contacts will usually pass electrical testing.


5 Methods to Confirm Contact Retention

 

1.   Operator Training: Push-Click-Pull Method

 
The IPC/WHMA A-620 Standard, section 19.7.5, reads in part: ..the 'push-click-pull' method of pushing a contact into the insert until the retaining mechanism clicks and then pulling on the attached lead until it is taut shall be used...
 

Advantages:

grey square  Easy, no tools required

grey square  Complies with IPC/WHMA A-620 Standard (for all classes when using crimp and insert style contacts unless other test requirements are specified)

grey square  No fixtures required


Disadvantages

grey square  No clear specification on Pull forces

grey square  Prone to Human error

Related Links:

grey square  IPC/WHMA A-620 Standard

 

2.  Pin-Sight Guided Assembly Tool With Contact Retention Verification

Cirris' new Pin-Sight tool guides operators to insert wires into the correct cavity and has a built-in force gauge that requires the operator to pull-back with a specified force in order to move on to the next wire.
pinsight-200
 

Advantages:

grey square  Easy to use--integrated with assembly process

grey square  Real-time. Immediate feedback on errors (error proof the process)

grey square  No fixtures required

grey square  Confirms clear push and pull forces


Disadvantages

grey square  Does not replace specific retention test requirements from the face of the connector


Related Links:

grey square   Cirris Systems Pin-Sight web page

 

3.  Contact Retention Hand Tools

Several contact retention hand tools are available for performing push-back tests one contact at a time from the face of the connector. Certain specs require this type of contact retention test (NASA)
cimg-tool300
 

Advantages:

grey square  Clear specification

grey square  Compliance requirement for NASA

grey square  No fixture required


Disadvantages:

grey square  Cost in labor time to check

grey square  Discovery of errors after assembly completed

grey square  Test one-contact-at-a-time after assembly


Related Links:

grey square   DMC Tools

grey square   Russtech Engineering

 

4.  Electrical Test With Spring Probes for Pushback

(Requires Fixture that moves probes into contact with connector contacts, then backs away)
Electrical test fixtures that use heavy pressure spring-loaded pogo pins can be used, but care must be taken to use a 2-stage fixture that fully engages the pogo pins, then backs them off slightly before the electrical test is performed. Otherwise the electrical test may still pass because pushed back pins may still be in contact with the spring probes.
push-test-b
 

Advantages:

grey square  Clear specification for retention from pin side of connector


Disadvantages:

grey square  Requires test fixtures for every connector

grey square  Insertion force increases with pin count (3 lbs x # of contacts)        

grey square  Requires mechanical levers or pneumatically operated fixtures

grey square  Requires 2-stage pneumatic fixture to 'contact then back off' (lower cost spring probes but more expensive test fixture)

grey square  Difficult to keep probes accurately positioned


Related Links:

grey square  www.lonestarindustrial.com

grey square  www.ectinfo.com

grey square  www.connect2it.com

 

5.  Electrical Test With Switch Probes for Pushback

 
(Requires costlier switch probes instead of standard spring probes)
Electrical test fixtures that use heavy pressure switch probes don't require the 2-stage fixture described above. Current flows in the switch probe only when the plunger is depressed enough to close the switch, so a pushed back pin will fail electrical tests with an open circuit. springprobe
 

Advantages:

grey square  Clear specification for retention from pin side of connector

grey square  Simplifies fixture engagement design. (Probe pins do not need to be backed off)


Disadvantages:

grey square  Requires test fixture for every connector.

grey square  Insertion force increases with pin count. (3 lbs x # of contacts) Requires mechanical levers or pneumatically operated fixtures

grey square  Switch probes are much higher cost than standard spring probes.

 

grey square  Difficult to keep probes accurately positioned.


Related Links:

grey square  www.lonestarindustrial.com

grey square  www.ectinfo.com

grey square  www.connect2it.com


Changes to Connector Design - Prevent Retention issues

  push-2-seat   1. Push-to-Seat Terminals with TPA: A push-to-seat terminal is a terminal that is inserted into the back of the connector cavity until it locks in place. Terminal Position Assurance devices are plastic inserts that keep these contacts in place after there insertion in the connector body. A TPA clip is the blue part in the photo on the left. These designs are 100% effective in eliminating chance of pushback. However, using this design requires inspection for presence of the TPA and also requires choosing a connector design that uses TPA styling. Often used by the automotive industry.
  pull-2-seat   2. Pull-to-Seat Terminals Pull-to-seat Terminals (requiring crimping after wire is inserted through connector body). This design is 100% effective in eliminating chance of pushback because the terminal cannot be pushed out through the back of the connector. The biggest challenges are with labor and equipment cost because termination occurs after inserting wire through the correct position of the connector body. If there is a miswire or broken contact in the manufacturing process, it requires cutting off the termination/contact to repair. Very time consuming!
  db09-250b  

3. Potting and Over-molding
Advantages:

grey square  Reasonably effective in preventing push-back


Disadvantages:

grey square  Does not ensure it is fully inserted at the time of potting/over molding (pin height problem)

grey square  Increased cost and labor

grey square  Prevents or hinders failure analysis and rework


Examples of Crimped-Pin Contact Retention Methods

  contact-lock-a   1. Friction or Interference Lock - the contacts fit very snugly into a hard rubber insert. Contacts are installed and removed by force using the proper tooling. The contacts are usually inserted from the rear of the connector and removed from the front (face) of the connector.
  front-release   2. Contact Lock - the locking device is located on the contact itself in the form of a spring finger which snaps into place on a ring inside the insert. The contacts are usually inserted from the rear of the connector and removed from the front (face) of the connector.
     front-release-2   3. Insert Lock - the contact has a ridge (shoulder) machined around the contact, which snaps into place in the spring clips (tines) that are located inside each cavity of the insert. The contacts are usually inserted from the rear of the connector and removed either from the front or rear of the connector.
The top contact, in the 'insert lock' illustrations (left), is shown in the "locked" position. The middle contact is shown with the tool probe or tip opening the spring clips. The bottom contact is shown as it moves out of the rear of the connector.
For more complete information on this topic follow this link to a PDF authored by: CMS (Connector Microtooling Systems)