Natalia: Thank you for your information.
Reards,
Bill
-----Original Message-----
From: Natalia Piedras <[log in to unmask]>
To: TechNet <[log in to unmask]>
Sent: Tue, Jun 5, 2012 3:46 pm
Subject: Re: [TN] Cleaning PCB Assemblies
Hello Bill,
We are successfully cleaning no-clean (when we absolutely have to) with our
Aqueous Trident Systems and we use Kyzen MX-2188 and Chemtronics ES197 Flux-off
remover.
I am also enclosing a presentation on frequency limits that you can download
from INDIUM website and
a summary of my notes when looking into the same issue:
-Is important to mention that RF signal propagation is affected not only by
material choices (PCB surface finish, Solder Paste, Wave Flux, Adhesive,
Underfills, Solder Mask, Moisture) and processing conditions (Reflow profile,
Cleaning Process, PCBA handling) but also by board design.
-Taking in account all these variables, in order to analyze the effect on signal
integrity of an specific “no-clean solder paste” over an specific “assembly” the
use of a “customized RF test circuit” is required; the most appropriate
personnel to develop this RF test circuit would be the RF Board Design Engineers
(R&D) along with the Test Department.
-Besides visual aspects this RF test circuit should measure signal leakage and
signal degradation taking into account the desired frequency at which the
specific assembly will be operating in order to simplify and narrow the process
research.
-Since different flux residues are created under different thermal conditions
the use of a temperature/humidity chamber is strongly recommended while reading
measurements during the RF circuit test.
-Regarding the use of lead-free solder paste merged with a cleaning process, the
contamination through the “parasitic-type capacitance” is no longer detectable
by ion-equivalent measurements alone since contamination levels are typically
below 1.5µg/cm2 , therefore all assembly line processes should be monitored and
results can be understood mostly only after the finished assemblies are “on the
field”.
-Regarding board design, to maintain signal integrity, the assemblies not only
require adequate insulation resistance, but also must have stable impedance. For
this reason, capacitive surface effects must be taken into account in the
circuit design.
-With frequencies higher than 1 GHz, the circuit designer must calculate even
the low resistance of conductive lines.
Natalia Piedras
Manufacturing Engineer
DORIGO SYSTEMS LTD.
Website: http://www.dorigo.com
Tel: (604) 294-4600 ext. 203
Fax: (604) 294-4609
E-mail: [log in to unmask]
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