All
A copy of the IPC 830 Handbook would probably assist you most as it describes - in some considerable detail - all that you could possibly want to know about this subject. The next revision will take you into another universe!
In short however, (please pardon the Deweyism) bubbles mean poor coating application / curing. As regards coating thickness, it should be as thin as possible yet pass your environmental tests.
There is a fairly simple method we have developed to "measure" coating thickness. We employ a special inspection microscope that our colleagues have developed with us that can focus on the coating and then on the substrate and measure the difference between the 2 focal points.
If anyone wants more info - you will have to beat a path to my ever-open door. Bring money and beer!
ATB - Graham Naisbitt - KBO
Email: [log in to unmask]
Phone: +44 (0)12 5252 1500
Web: www.gen3systems.com
On 14 Jul 2011, at 16:36, Bush, Jeffrey D. (US SSA) wrote:
> Bubbles can be caused by these conditions as well as a host of other variables. While the experiments are going in to drive the factors to ground you should assess if you have bridging or not The intention of the term indicates non-isolation of devices - generally if you see a series of bubbles the thickness is adequate as you can discern CC between the gaps = coverage. The test for a large event must be to break and assess the coating integrity.
>
> Jeffrey Bush
> BAE Systems Incorporated
> Electronic Systems Division
> IS&R - Space Products and Systems
> P.O. Box 868, MER24-01G43
> Nashua, NH 03061-0868
> Office +1 603.885.8137
> Mobile +1 603.318.8056
> Fax +1 603.885.5258
>
>
> -----Original Message-----
> From: Temkin, Gregg [mailto:[log in to unmask]]
> Sent: Thursday, July 14, 2011 10:36 AM
> To: [log in to unmask]; Bush, Jeffrey D. (US SSA)
> Subject: RE: [TN] IPC-A-610 Conformal Coating - Coverage
>
> How would you determine that you "...still have the minimum thickness on the conductor..." to allow you to say breaking (cured?) bubbles is OK? It's awfully difficult to measure conformal coat thickness on the sides of DIP leads or solder joints.
>
> IMO the bubble bridging requirement is clear. If there's a bubble bridging between adjacent leads, it's a defect for Class 3. If you break the cured bubble, you're performing a repair, unless it's in your process to do it that way, but again, it's risky because you don't know if the leads or solder joints that were formerly in the bubble are truly coated.
>
> I would fix the process to fix the problem. Bubbles can be caused by excessive application thickness or putting coated boards in a curing oven too soon after, or coating warm boards and a few other reasons that would be specific to the conformal coating system.
>
> Gregg
>
> -----Original Message-----
> From: Bush, Jeffrey D. (US SSA) [mailto:[log in to unmask]]
> Sent: Thursday, July 14, 2011 5:39 AM
> To: [log in to unmask]
> Subject: Re: [TN] IPC-A-610 Conformal Coating - Coverage
>
> Bridging would indicate a reduction in the minimum surface coating requirement on either end. So it you break the bubble and you still have the minimum thickness on the conductor you are OK.
>
> Jeffrey Bush
> BAE Systems Incorporated
> Electronic Systems Division
> IS&R - Space Products and Systems
> P.O. Box 868, MER24-01G43
> Nashua, NH 03061-0868
> Office +1 603.885.8137
> Mobile +1 603.318.8056
> Fax +1 603.885.5258
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Lum Wee Mei
> Sent: Thursday, July 14, 2011 3:34 AM
> To: [log in to unmask]
> Subject: [TN] IPC-A-610 Conformal Coating - Coverage
>
> Dear All,
>
>
>
> Can some kind souls help me to interpret the below statement taken out
> from IPC-A-610 Section 10.5.2.2 Conformal Coating - Coverage? I am look
> at Class 3 and I am loss on its interpretation, especially 'Voids or
> bubbles'.
>
>
>
> Acceptable - Class 1, 2, 3
>
> No bridging of adjacent lands or conductive surfaces from :
>
> * Loss of adhesion (mealing)
>
> * Voids or bubbles
>
> * Dewetting
>
> * Cracks
>
> * Ripples
>
> * Fisheyes or orange peel
>
>
>
> It is common to find bubbles trapped between the soldered leads of those
> gull-leaded components and between closely mounted SMDs passives for
> brushing method. Are these bubbles allow for Class 3?
>
>
>
> Thanks and regards,
>
> ~wee mei~
>
>
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