A couple of comments to Doug Pauls' posting on ionic contamination due to
no-clean fluxes:
Ion chromatography provides a quantitative assessment of those ionic species
in an extract. One key issue is the extraction methodology - time,
temperature, and extraction medium, as well as the part of the
board/assembly that is being extracted. Simply using 2.3.28 can lead one
astray - see the presentation I gave at the Fall 1997 IPC Bare Board
Cleanliness Task Group Meeting (detailed in the Fall 97 minutes, page 86).
This case study showed that the results from method 2.3.28 were NOT
predictive of field performance. It is important to use electrical testing
in combination with extractive analyses.
No-clean fluxes have been used successfully for ~ 10 years. There are
specifications in place (e.g. Bellcore) that allow for production of
assemblies that can meet the reliability requirements of the
telecommunications industry.
John Sohn
Lucent Technologies - Bell Labs
> ----------
> From: Douglas Pauls[SMTP:[log in to unmask]]
> Reply To: TechNet E-Mail Forum.;[log in to unmask]
> Sent: Tuesday, October 13, 1998 2:12 PM
> To: [log in to unmask]
> Subject: Re: [TN] FW: [TN] Ionic Contamination due to No-Clean Fluxes
>
> > Doug,
> > It will help if you would post your opinion on the TechNet.
>
> OK. I've been off the Net for a while working on other projects that
> demand
> WAY too much time.
>
> As I understand it, here was the original question:
>
> > I have a customer who is concerned about Ionic contamination due to
> > bromines/bromides. I have explained to the customer that the flame
> > retardant in FR-4 material is based on bromine. Also, the flux that we
> use
> > for the HAL is Hydrobromic Acid based, this is used instead of
> Hydrochloric
> > Acid based flux to cut down on the chloride contamination.
>
> Dave Hillman, a relatively sharp dude, kicked in:
>
> > Hi Scott - The bromines/bromides that are a component of the FR4 flame
> > retardant chemistry TYPICALLY don't cause electronic assembly problems.
> > Give Doug Pauls at CSL Inc. an email ([log in to unmask]). Doug is heavily
> > involved with ionic contamination from both the IPC technical
> committees
> > and an electronics assembly residue analysis standpoint. Good Luck.
>
> Here's my 2 cents worth:
>
> Bromide material is found in a wide range of electronic materials,
> primarily
> laminates and some solder masks. Bromide, as a flame retardant, is added
> to
> these materials in order to gain the UL 94 V0 flammability classification.
> The amount of added bromide will vary greatly between different laminate
> makers: Norplex Oak will have one level, Rodgers another, Allied Signal
> yet
> another.
>
> If you analyze a laminate using the IPC ion chromatography procedure
> (method
> 2.3.28), you would typically see 0 -7 micrograms per square inch of
> bromide.
> Exposures to reflow temperatures will increase the porosity of the
> laminate
> and mask, allowing more bromide to be extracted. After 2-3 passes to
> reflow,
> bromide levels can go as high as 10-12 micrograms per square inch. When
> bromide levels start to go appreciably higher than this, it is indicative
> that
> a brominated flux was used, such as the hydrobromic acid mentioned above.
>
> Like any halide, bromide can be detrimental when found in high enough
> concentrations. How high is "too high"? I can tell you that for "a
> nominal
> fee" <grin>.
>
> We do a great deal of process troubleshooting using ion chromatography.
> In
> our experience, when bromide levels start to rise above 14-15 micrograms
> per
> square inch, you approach the "danger zone". The higher you go in bromide
> concentration, the greater the risk of electrochemical failures
> (corrosion,
> metal migration, electrical leakage). Typically speaking, most bare
> boards
> run through a brominated HASL line will range anywhere from 12 micrograms
> per
> square inch (fairly clean) to 40-50 micrograms per square inch (fails REAL
> fast). We've seen it go as high as 80-100 micrograms per square inch
> (fails
> before it starts).
>
> HASL fluxes come in one of three flavors: chloride-laden (e.g.
> hydrochloric
> acid); bromide laden (hydrobromic acid), or laden with both. Many
> fabrication
> houses use one or more of these and you may never know if you are getting
> a
> chloride board, a bromide board, or a board with both.
>
> Which is worse? Chloride by far. As a more electroactive material,
> chloride
> does far more to start and perpetuate electrochemical failures than does
> an
> equivalent concentration of bromide. So an HBr HASL flux is marginally
> "safer" than an HCl HASL flux. Both are marketed as water soluble fluxes,
> but
> have a BIG difference in water cleanability. Tap water is a lousy cleaner
> in
> general, but chloride is more easily cleanable than bromide. Bromide flux
> residues tend to be bulletproof to water cleaning. In our experience, to
> effectively reduce bromide you need all deionized water cleaning with a
> small
> amount of saponifier.
>
> We have seen some, shall we say less ethical, fabricators switch to a
> brominated flux because bromide residues will typically not show up in a
> ROSE
> test (e.g. Omegameter). The bare boards, by conventional standards, look
> cleaner. There are, of course, perfectly valid reasons for switching to a
> brominated flux. I don't want to paint all fabricators as villians.
>
> The residues on the bare boards have an impact on the assembly process,
> but a
> critical impact for a no-clean assembly process. Fabricators who supply
> no-
> clean assemblers need to check the cleanliness of the boards by ion
> chromatography, as do assemblers who are doing no-cleans.
>
> Well, time to climb down from my soapbox.
>
> Doug Pauls
> Technical Director
> Contamination Studies Labs
>
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