IPC LF & TN news from late September to early October

And here are some more interesting tidbits from the IPC’s Technet & Leadfree lists, from September 29 to October 3, 2006.

  • There was a question about tests for hexavalent chromium. This is still a very thorny issue because RoHS bans hexavalent chromium (Cr6), but trivalent chromium (Cr3) is still okay; however, most tests that quickly detect chromium detect only chromium and don’t differentiate between trivalent & hexavalent chromium.

    John Sieber from NIST put up a post saying that the test being developed by IEC TC111 Working Group 3 only detects the presence of hexavalent chromium, and not the concentration.

    Furthermore, many of the tests that are used by various standards organization, such as IED, EPA, ISO, DIN, etc., were each developed for a specific type of coating. So if a test was developed for hexavalent chromium coatings on aluminum and is now used on trivalent chromium coatings on steel, there is probably no way to correlate the values from the test with the actual amount of hexavalent chromium present in the finish.

    So, to make a long story short, the search for a quick, reliable, cheap, and quantitative hexavalent chromium test was still ongoing as of late September.

  • In a related post, John Sieber posted some more information regarding the EPA tests for chromium.

    After a brief exchange with Denis Ryskamp, I can say the following about EPA 3060A and 7196A

    Neither 3060A nor 7196A apply to passivation coatings on alloys.

    3060A may be subject to a positive bias (false positive) if the digestion conditions cause oxidation of Cr3.

    7196A is calibrated from 0.5 mg/L to 5.0 mg/L (mg/L = ppm by volume which is different from ppm by weight or mg/kg when solution density is not equal to 1.0 g/mL)

    7196A is not applicable to solutions in which the Cr6 cannot be detected by a UV spectrophotometer. The scope range is 0.5 mg/L to 5.0 mg/L period. For this reason alone, the method would be invalid even if the sample type falls within the scope concentration range.

  • A question was asked about using visual inspection to look for symptoms of excessive contamination of the solder pot in a wave solder machine. The response from another member of the list was that if the problem is poisoning of the solder pot, then by the time it’s affecting the joints on a visible level, the line will have to be shut down. It’s a much better idea to do regular testing of the solder pot if your goal is catching the problem while it can still be remedied without completely shutting down the line (and maybe even doing a product recall).

  • There continue to be problems reported with new(er?) PCB laminates in the new higher-temp lead-free soldering processes. Werner Engelmaier wrote a very good paper about PCBs going through the lead-free process and the specifications to look for. It’s definitely not free, but I’ve read it and found it to be worth the price. I learned a lot from reading it.

  • Related to the previous topic, here is a quote from a post by Valerie St. Cyr, which indicates our problems are only starting:

    There are materials whose properties’ data sheets have the values that would indicate high thermal stability, and so one might conclude they could pass a lead free reflow or reflows. But it is not so simple. As the laminators load up on fillers to restrain the Z-axis CTE to mitigate against the higher temperature at reflow, the interlaminar strength can be compromised. We are seeing an x-y sheer phenomena. The delamination is not prepreg to copper, or adhesive failure, it can be within a core, or prepreg to glass – a cohesive failure.

    Also, regardless of the above, your particular design might survive a lead free reflow process while another design on the same material fabricated by the same supplier will not. Some of these materials have design dependencies only now being understood.

    OK, if that isn’t problematic enough, these materials aren’t drop-in replacements in the fabricator’s processes despite any claims to the contrary from the laminators. So, for the same design on the same material if you switch fabricators you could then experience delamination or massive hole wall pullaway (which we haven’t seen in a very long time).

    What else ? Oh yeah, for non-phenolic systems better prebake before assembly …

    What else ? Oh yeah, some (not all, but some) are still being tweaked and what worked last month may not work next month.

  • Lee Parker wrote an article for PC Design and Fabrication (maybe in the August issue?) about moving an establish PCB assembly from leaded to lead-free processes. I don’t have the URL and haven’t read the article, but I know that any time I’ve seen Lee Parker post on the IPC lists, his information has been very worthwhile.

  • Posts from Jeffry Bush of Vermont Circuits Incorporated are also always informative and worthwhile.

  • Here is a link to an article in the September 28th, 2006, issue of electronicsweekly.com. The article is by Steve Bush and is titled “Will the US market play hard-ball over RoHS?” The article concerns a statement by Newark InOne calling for a federal version of RoHS to be enacted in the U.S.

    While I can sympathize with Newark InOne’s dread of dealing with 50 different version of RoHS, enacted bit-by-bit and with 50 different deadlines by all 50 U.S. states, I doubt they realize the amount of ill will they are generating within the U.S. electronics industry.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s