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flow thru

David Vulcano


flow thru | 29 October, 1999

We are placing several axial components that have STEEL leads. Have noticed that the steel components do not get good flow thru(we manufacture to IPC-A-610 Class II Standards which reqires 75% flow thru)

We are using Seho Wave Machines with Nitrogen atmosphere as well as fluxing the bottom side of the board. We have found manually spraying the top side of the board (with a spray bottle) helps somewhat.

I am looking for some data or information (past SMT articles, Web sites, etc.) that explain the soldering/flow thru issues associated with steel leads.

Many Thanks!

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Re: flow thru | 30 October, 1999

David I have recently taken the IPC-A-610B instructors course and according to the teacher the revised addtion is suppose to be 50 percent fill in plated thru holes

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Re: flow thru | 31 October, 1999

David: I think it's great that you are getting that much barrel fill with STEEL leaded components!!! So, what kind of steel are the leads are made from? How much corrosion is on the leads?

Frankly, I don't believe that the leads are made of steel. I think you have a solderability problem and should determine its source.

1 How do these component leads solder when not on the board? 2 How does the board solder with no components? 3 Tell us more about the breadth of the problem: Same components/different board, new problem/old problem, etc 4 What should we know about your flux type, fluxer, preheat, conveyor speed, solder pot temperature, etc?


Dave F

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dave r


Re: flow thru | 1 November, 1999


Have the class III requirements changed?


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Jim Snipes


Re: flow thru | 1 November, 1999

Dave thaanks for your quick reply. The flow through probelm exists on several component, Examples; small Tan electolic caps.,electrolic epoxy caps. and one specfic lad on a resistor network. I have veried conveyor speed and readjusted heat sett ings closer to manufacturing specs for flux. Flux type is AIM 264-5 no clean applied by spray. Solder heat is at 250c. The reflow probelm is isolated leads and not one particular area. I really think it's a component corrosion problem. There are two power diodes with steel leads. Most of the time these do solder with no problems. Ant other sudggest will be helpful. Jim Snipes Process Engineer

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Mark W.


Re: flow thru | 1 November, 1999

Jason, What is the revision of IPC you are referring too??

IPC 610 rev. b requires 75% fill on classes 2 & 3. Class 2 does allow the exception of 50% fill if the PCB has a Metal Core or Thermal/Heatsink Plane provided that the solder extends 360 degrees around the lead and there is 100% wetting from the barrel walls to the lead on the solder side. See Section 4.1, figure 4-2 for exact wording.

Please let me know if this is changing and when it goes into effect. Thanks, Mark

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Re: flow thru | 2 November, 1999

Jim: Several points:

1 If you�re correct about corrosion of your component leads (which is entirely possible if the leads are steel, as you say), then the AIM 264-5 no-clean may not be aggressive enough to remove the corrosion you are seeing routinely. Check with your supplier on that possibility. 2 When you say the problem is wide-spread (ie, small tan electrolytic caps., electrolytic epoxy caps. and one specific lead on a resistor network," in addition to the steel leads on the "two power diodes"), it makes me wonder if there isn�t a broader process or board design problem.

Continuing to think about a process problem, you say that you "verified conveyor speed and readjusted heat settings closer to manufacturing specs for flux." Certainly it�s a first good step to have your wave solder thermal profile lined-up with the requirements of you flux, but for this board

� Is your flux air knife set to give proper barrel fill with flux, especially on the problem components? � Is the flux manufacturer�s recommended amount of flux on the board when it is conveyed to the preheater? � Does the top-side board temperature, just as it moves to the wave, match-up with your supplier�s recommendations for the thickness of board? � Is the board dwell over the wave sufficient to get proper hole fill?

If these things are correct and you still have a problem with hole fill, the board layout may require review.


Dave F

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Re: flow thru | 2 November, 1999

You appear to have two problems working against you at once. One is component lead corrosion that the no clean flux isn't aggressive enough to remove. Do a simple dip and look test. Flux the leads of a component and dip it into the molten solder for 3-4 seconds. If it doesn't wet - the part is at fault. Specific leads on a resisitor network could be poor capillary action of the flux in that area caused by a clogged fluxer nozzle. A bare board with thermal fax paper on top would prove that out. No black dot in a hole = no flux in the barrel. The other possibility is heat transfer. If the lead and barrel don't get up to solder temperature (361F) then the solder will freeze in the barrel before it makes its way to the top.You can thermocouple the lead on top and measure the temp as it goes through the wave. Remember the board may see 200 in the preheaters but has only 1-2 seconds in the wave to get to a min of 361F. Ray

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