My limited experience with hipot testing of 120 VAC devices (heaters,
thermostats) in a past life also showed that an item failing a hipot test
would fail again at a lower voltage.  This is likely due to organic
dielectric materials being partially converted to carbon in the voltage
path, thus creating a path of lower resistance.  I would not trust the
reliability of a device that has failed a hipot test.


Dave Roach
Trane GCC
4833 White Bear Parkway
St. Paul, Minnesota  55110
651-407-4294

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jeffrey Bush
Sent: Wednesday, October 06, 2004 9:33 AM
To: [log in to unmask]
Subject: Re: [TN] High Voltage Test Risk of Damage

I have seen issues similar to this. Generally leakage from SMT features
that are inside the minimum spacing for that voltage as well as other
isolated areas that are exposed to the surface environment.  This should
not be seen on nets isolated by dielectric materials - unless the
spacing is within the minimum withstanding voltage values for the test.
Failed dielectric is prone to latent issues during duty cycle as the
specific failed area no longer provides the dielectric properties of the
material.



Jeffrey Bush
Director, Quality Assurance and Technical Support

                          76 Technology Drive - POB 1890
                             Brattleboro, Vermont 05302-1890
                                Tel. 802.257.4571.21 Fax. 802.257.0011
                                    [log in to unmask]
                              http://www.vtcircuits.com



-----Original Message-----
From: Anslow, Phillip [mailto:[log in to unmask]]
Sent: Wednesday, October 06, 2004 10:23 AM
To: [log in to unmask]
Subject: [TN] High Voltage Test Risk of Damage


Dear TechNeters,
If a PCB is Electrically Tested at a higher voltage than circuit was
designed for in terms of isolation spacing between tracks, what would be
the risks to the PCB and subsequent use? I have had a batch tested at
higher than specified voltages on all nets and some failed. On
requesting a retest at specified voltages on nets as specified, the
majority have passed. Has anyone experience of the failure modes or
latent defects this may have introduced? Thanks in advance, Phil Anslow.

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