[SI-LIST] Re: Rigid-Flex Testing

  • From: "Jackson, T L" <t.l.jackson@xxxxxxxx>
  • To: SI-List <si-list@xxxxxxxxxxxxx>
  • Date: Tue, 21 Oct 2003 15:38:48 -0700

I want to thank those people who responded to my first email.  All of their 
suggestions have merit, but are problematic one way or another at this stage.  
I should have added more detail in my previous email.

My subcontractor has a (1) backplane that has two flex sections so it can be 
bent into a "U" shape for installation in a chassis.  So along the length of 
the board, it starts rigid, goes through one flex section, a rigid center 
section, another flex section, and ends with a rigid section.  There are 
ninety-six (96) traces total that pass across one or the other flex sections.  
The flex sections are 1 oz/ft^2 of copper, double-sided, on a 2-mil polyimide 
film, with a 1-mil polyimide film coverlay on each side of the exposed areas.  
This backplane has been assembled, i.e., it has active and passive components 
on it.

One (1) trace has found to be broken and has high resistance (Ohms versus 
Milli-Ohms).  That break was located by thermal imaging, since X-rays did not 
reveal the break.  It was about 1/3 of the way into the center of the flex and 
not at the outside edge where it would be suspected.  It was at the rigid-flex 
interface as was expected.

Now, our customer is suspicious of all of the other 95 traces in the flex 
sections.  I am trying to find ways to check the remaining traces before using 
this backplane in a Qualification unit.  

My subcontractor is presently making four-wire resistance measurements to check 
the remaining traces.  Based on the X-rays we have seen, our subcontractor does 
not have the capability to produce X-ray images that will show a break.  TDR 
might work.  But since each trace is a different length, it will be difficult 
to determine whether a reflection is from a partial break or from a via near 
the edge of the rigid-flex interface.  Thermal imaging might work, but we have 
to be careful to not damage any components.

I was hoping that someone on SI-List would have another suggestion that would 
better than these.

TJ
Thomas L. Jackson, P.E.
Senior Staff System Engineer
Department L1-50, Remote Sensing System Engineering
Lockheed Martin Space Systems Company
Building 149
1111 Lockheed Martin Way
Sunnyvale, CA  94089
Telephone:  (408) 742-2013
Facsimile:  (408) 742-7701


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