If you see something disturbing, take off your glasses, and alás, the ugly thing isn't there any more. The question about magnification is discussed daily and everywhere. I understand your perplexity. My view: The important question should not be what magnification you use. Instead you should ask yourself whether this amount of solder splash is bad or not for the reliability. To forbid ANY solder on the gold fingers would be a exaggeration. Next question ought to be why solder is forbidden at all? It seems as we need take a further step backwards. Why is there gold on the fingers? Why not tinned fingers? I've seen and examined thousands of boards the last three decades. Both gold plated and tinned. In general, they are compatible and equal. In very harsh environment, gold plated fingers win because gold is 'inert' . Another reason for using gold is the lower and more reliable insertion resistance if you plug in /out frequently. If you don't do that, tin may work good enough because of the hermetic micro connection you get. So, tin is not a enemy but a possible member. Like gold, also tin works as a 'lubricant' when the connector forks slide over the fingers. Also like gold, tin creates hermetic micro connections, which is a condition for longlasting low ohmic resistance. If small amounts of tin exist on the fingers, there will be no problems. With some exceptions. Namely a) the tin may include fluxes b) the tin may not be flattened under the sliding contacts but pushed aside, loosen and become a dangerous debris that can cause electrical shorts. This was a short view upon the basics of tin contaminating gold. Will I come to any conclusion? No. It's YOU that must come to a decision, possibly with the above in mind. To refuse a batch of extremly expensive MIL boards because of a nearly invisible amount of tin would be madness, as well as accepting hundreds of solder paste spheres that will jump around. As always, Dough's 'it depends' is a good start before give instructions to the operators. By the way, there is a further reason for not follow the standards thoughtlessly : optical dispersion between individuals. There are guys who have hawkeyes and those with weak sight. The former notice lots even without a microscope, while the later does not observe anomalies even in a microscope. I can see your impatience (' Gosh! He is talking and talking and never comes to the point...) so I round up with recommending that you read a few pages I send offline, from Puligandla Viswanadham's book " Failure Modes and Mechanisms in Electronic Packages. He has a table with factors that have impact on connectionsand contacts in general, and tin spots on gold is not even mentioned ( not saying that his book covers everything ). Standards are like medicines, we need them but they should be used correctly. I can hear your relief ( 'My goodness, he is ready...) Good Luck Inge On 20 April 2011 22:13, Kelly Morris <[log in to unmask]> wrote: > I am looking for some discussion on acceptability of solder on gold fingers > per IPC-A-610. > I've searched the archives and have not found my answers there. > > IPC-A-610, section 10.1, page 10-3 says: > Solder, any metal other than gold, or any other contamination in the > critical contact area of the fingers is a Defect - Class 1,2,3. > > At face value, I would interpret that to say that ANY solder found in a > visual inspection on a gold finger would be considered a defect. > > The solder we are seeing is from indiviual solder spheres from the solder > paste and are being missed by the assemblers and process inspectors. They > currently believe that if the solder contaminate on the gold finger is not > visible with a 4x magnifcation, it is not a defect. > > The gold fingers under inspection are designed at .040" wide. > There is one QFP on the PCA that has solder pads that are .011" wide > > My question is.....To inspect the gold fingers and determine if a PCA is > defective or not.....What magnification level is appropriate when inspecting > these gold fingers. > > Information/Discussion: > Per table 1-2 on page 1-6, suggests for lands > 0.0394 a Magnification for > inspection of 1.5x to 3x with a max referee of 4x. > > However, the last sentence of paragraph 1.8 on page 1-6 states "For > assemblies with mixed land widths, the greater magnification may be used for > the entire assembly. > > If this PCA has some land widths designed at .011" wide, then according to > the last sentence of paragraph 1.8, I would say that per table 1-2, an > inspection magnification of 7.5x to 10x with a max referee magnificaton of > 20x would be appropriate, and any solder that is visible on a gold finger at > that magnifcation level is a defect. > > Is my interpretation flawed? too stringent? 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For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 16.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------