Kevin,
Besides the two the two conditions (Class of Product and Environment) David listed you need to keep in mind the order in which you use the fluxes. In David's case doing water soluble flux assembly and cleaning prior to the use of rosin or no-clean you should be okay because there should be no water soluble flux residues to worry about. My background is in the telecommunications industry and Bellcore/Telcorida did not allow us to use water soluble flux for wave solder assembly after we did topside surface mount with or Bellcore compliant rosin based solder paste. Since we used Bellcore compliant solder paste (i.e., compliant in that it passed all Bellcore reliability tests if left behind and not cleaned) they were worried that some of the water soluble flux could be trapped in the compliant rosin flux residue left form the topside assembly and wouldn't be completely removed during a cleaning process and could therefore be released during the life of the product if the rosin softened during a use temperature increase.
Regards,
George
George M. Wenger
Reliability / FMA Engineer
Base Station and Subsystems Group
Andrew Corporation, 40 Technology Drive, Warren, NJ 07059 (908) 546-4531 [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David Tremmel
Sent: Monday, October 03, 2005 1:32 PM
To: [log in to unmask]
Subject: Re: [TN] Mixing Fluxes: Water Sol and Rosin
Kevin,
That depends on the class product you are building/repairing and what kind of environment your boards are used in.
I have used water-soluble flux and then a rosin or no-clean flux afterwards for touch-up work and it really comes down to cleanliness. If the water-soluble flux residue is removed thoroughly, then it should not be a problem using a different flux for touch up, but as it has been said, it depends (sorry for any copyright infringement).
What I recommend is do your own tests. Examine any field failures which have been previously reworked and look for any corrosion or residues in the reworked areas. Although the reworked area may appear to be clean (using a microscope), sometimes any undesired residues are not seen until a unit has been in the field for a while.
The gurus with the chemical degrees and the millenia of experience can probably explain it better.
Ramon, you're a sharp cookie with a lot of experience, care to chime in?
David
>From: Kevin <[log in to unmask]>
>Reply-To: TechNet E-Mail Forum <[log in to unmask]>, Kevin
><[log in to unmask]>
>To: [log in to unmask]
>Subject: [TN] Mixing Fluxes: Water Sol and Rosin
>Date: Mon, 3 Oct 2005 11:34:53 -0500
>
>Is it acceptable to mix flux types on a single piece of hardware? I
>have background in MIL/AERO requirements of the "rosin only" creedo.
>My past experience is with rosin types only, to avoid all the emotional
>customer issues and testing requirements. However, I am now working
>for a company and their SOPs dictate use of WS at first solder,
>followed by water clean. They then dictate rosin for any touchup, with
>hand clean only. Is there a risk in mixing water sol and rosin on a single piece of hardware?
>What about resin and rosin?
>
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