Date: Fri, 07 May 2010 20:52:01 -0400
From: Kevan Hashemi <hashemi@opensourceinstruments.com>
Organization: Open Source Instruments
To: Josh Bourassa <Josh@aapcb.com>
CC: Chet Williams <Chet@aapcb.com>
Subject: A3019A Test Completed

Dear Josh,

Here is a list of problems I discovered with the 9 boards you sent me.

(1) I removed U1 (A1171 in DFN-6) on 8 boards. In 6 cases, I saw no 
solder on the pin 3 pad, other than the tin plating applied by the PCB 
manufacturer.

(2) After I re-apply U1 with no-clean flux on 5 of the boards, U1 
functions correctly for a while, but if I cool the board by cleaning it 
with dichloromethane or alcohol, or if I cool it with freezer spray, it 
will stop functioning and remain non-functional until I have heated it 
with a heat gun. I observed erratic behavior like this in U1 during my 
prototype construction. U1 is sensitive to heat. I notice that one of 
the 10 boards in the panel was badly burned. If you heated the remaining 
boards to 600 F (300 C), U1 would be damaged, resulting in the erratic 
behavior I see today. I cannot replace U1 today because I sent all I had 
to you. But I might order some and confirm my hypothesis.

(3) In 1 board, I removed U6 because the power supplies were shorted. I 
saw that the solder paste beneath the BGA-56 package was smeared, 
causing the short.

(4) On 2 boards, I see 50 uA excessive consumption when active. I 
suspect a short between balls under U6, the BGA-56, but I have not 
removed U6 yet to check.

I have 3 working boards with fully-functional U1 and all other circuits 
working correctly. I had to re-work U1 on 2 of these boards, but the 
other one worked first time with no rework, and survives freezing and 
heating cycles.

So, it appears that there were three problems during construction.

(A) There is not enough solder on pad U1-3 (DFN-6).

(B) Most of the boards were over-heated and U1 was damaged.

(C) In at least one case, the solder paste was smeared beneat U6 (BGA-56).

Was the board to floppy for proper placement of parts? If so, you may 
have had to do some re-work, and it's clear that something went wrong in 
the re-work.

What do you want to do now?

Yours, Kevan

-- 
Kevan Hashemi, President
Open Source Instruments Inc.
www.opensourceinstruments.com