×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

I need a test for microcracking in diodes

I need a test for microcracking in diodes

I need a test for microcracking in diodes

(OP)
We are having major problems with rectifier diodes (70 amp 200 volt DO5 devices).  We are testing for solder voids by measureing heat retained in the diode after a power pulse, contamination and general construction by a biased temperature cycle.  However we do not have a good test to detect microcracking that was found by an analisys house.  Does anyone know of a good fast test?

RE: I need a test for microcracking in diodes

Is there a problem associated with the microcracking?

TTFN



RE: I need a test for microcracking in diodes

(OP)
With load and temperature cycling the cracks tend to grow leading to complete device failure.

RE: I need a test for microcracking in diodes

Then, you're going to have to trade off some life to weed out the bad parts or beat up the supplier.  They simply should not be supplying parts with microcracks.  It's absurdly expensive to facilitize for weeding out something that shouldn't even be there.

If you're insistent on testing, then you'll need to run an accelerated life/thermal cycle and measure the appropriate indicator, presumably the leakage current.

This would most likely chew up a sizeable number of otherwise good parts to refine the test process.  You'll most likely also cause premature failure on parts that would have otherwise been fine in normal service.

TTFN



RE: I need a test for microcracking in diodes

I have never tried this, but read about it for finding cracks in PCB traces.

Inject a high frequency signal on the trace and run a scope probe along the trace. The signal supposedly attenuates or alters in some way down stream of the crack.

Maybe some permutation on that will work.

RE: I need a test for microcracking in diodes

(OP)
Thanks Kontiki99,
I will keep the idea in mind, but it is not practical in this case since the diode is about 3/8 inch square and sealed inside a metal hermetic housing.

IR stuff,
I know we shouldn't have to do this much sorting, however there are not many manufacturers that make big power diodes in metal cases anymore, and even fewer we have not had problems with.  We are working with the supplyer and attempting to qualify new suppliers to meet our needs.  As a matter of fact the thermal cycle testing you mention is part of our qualification process and is done on a production basis for a couple of products, so far with no decrease in product life.

RE: I need a test for microcracking in diodes

in the mixer diode quad demage by ESD the noise figure measurement is used to determin if the diodes are in tack of not. not sure that will apply to high power diodes.

kontiki99
Your approch might have sense, hoever I will use reflectometry or reflection in time domain. You shoud see some dicontinuity in the time /distance from the source.
So some network analyzer with time domain could be used for that.
You will used good unit as a standart how the time domain signal should look like and compare that to demage component. The demage component will propably have a lot of more spiks a dips then the good one.
 

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close