> 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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