One for me please.

PG

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Message du 07/06/12 13:12
De : "Charming Chan" 
A : [log in to unmask]
Copie à : 
Objet : Re: [TN] Cleaning PCB Assemblies

Natalia, a copy to me？Thanks！ Sent from Huawei Mobile Natalia Piedras 编写： >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] ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ 

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