I believe you should use the die area for the calculation (normally, cut
off the PCB outline, just leave the die area = white outline of the chip
area for extraction). If you use PCB area, you will pass the ROSE, and
possibly still fail reliability test (under the chip may still got high
conc. Of residual, but average over the board area, you would be OK)....
Depend upon who you want to fool...you find it now, or later... Your
choice...;-)
jk
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of
>Brian Ellis
>Sent: Friday, May 23, 2003 12:06 PM
>To: [log in to unmask]
>Subject: Re: [TN] ROSE for Flip Chip
>
>
>Glenn
>
>I agree that using the die area would give a larger value, but
>are you sure that you can discount the PCB area. Have you
>measured the PCB, by itself, before attaching the die, and,
>with no die/flux but after cleaning? Remember the fact that
>putting the flux only on the die is meaningless because it
>will spread over the PCB well beyond the condines of the die
>area during reflow.
>
>Brian
>
>Glenn Pelkey wrote:
>> Hi Technetters,
>>
>> My buddy and I have a disagreement on using Resistivity of
>> Solvent Extract (ROSE) for measuring cleanliness on a Flip
>Chip board.
>> So, we're throwing it to league of experts on this forum for feedback
>>
>> Here's the story: The board and assembly are very simple.
>> One flip chip die at about 0.002 square inches and one board about
>> 0.490 square inches. Flux is applied only to the flip chip die,
>> reflowed, and DI inline washed.
>>
>> Here's the disagreement: I say use 2X the surface
>area of the
>> die for the calculation. My good friend says use 2X the board
>> surface. Of course, you can see one number is much higher than the
>> other in ug/sq inch NaCl equiv. My logic for using only the
>die area
>> is to understand the process cleanliness at that location
>only, but I
>> recognize the entire board surface could be cross
>contaminated in some
>> manner. We also loaded the machine with 32 of these units to get
>> something measurable. When we only put 4 in, nothing showed up, but
>> the smallest entry for surface area is 0.1 square inches.
>>
>> Thanks for your input!
>>
>> Glenn
>>
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