Lpc2000

Thiadmer Riemersma (ITB CompuPhase) wrote:

>Hello everyone,
>
>On 8 december 2005, Brendan Murphy posted a report where switching a
>pin from GPIO to EINT (external interrupt) caused an edge-triggered
>interrupt (message http://groups.yahoo.com/group/lpc2000/message/11212).
>
>I replied to that message saying that we encountered precisely that
>error on a single PCB out of 20 that we tested. Our hypothesis was
>that the particular PCB had some kind of defect. This hypothesis was
>based on the fact that the spurious interrupts _disappeared_ when
>slightly bending the PCB.
>
>We recently encountered a second board with exactly the same problem.
>Here, too, pressure on the board influenced the occurrence of spurious
>interrupts. Also similar was that the "pressure point" was on the
>processor. In a related test, we heated the processor. This also
>influenced the occurrence of the spurious interrupts.
>
>We replaced the processor on the board (an LPC2138) by another one. No
>more spurious interrupts occurred.
>
>We are wondering whether this issue may perhaps be caused by the
>processors not being handled correctly during manufacturing (perhaps
>there was no baking before reflow soldering).
>
>  
>
Well, it is tough to assume that everything else was okay.  In another 
posting I made this morning was about how clean the finished board was 
and your comment that replacing the chip brings it to mind.  I had a 
manufacturer call me in to try to find a problem with a group of boards 
that they could not get working.  These had been assembled in Asia and 
the majority of the lot worked, all but these few boards.

Looking at these boards under a 20X microscope, I discovered solder 
debris which had not been properly cleaned from the board.  There were 
tiny groups of solder balls + unmelted paste around many of the pins.  
The cleaning process had removed the majority of the debris around the 
pins but failed to adequately remove it from "underneath".  The debris 
was tucked up on the "inside" of the pins where it was difficult to see.

Several of the boards worked when I just reheated the pins with a 
soldering iron and reflowed the debris.

TomW

-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
----------------------------------------------------