Water Washing

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Here is my question to the Guru's on this site. Lead free... - Dec 21, 2009 by BoardHouse

1) I'm not familiar with the acronym CAF. Could you spell th... - Jan 04, 2010 by cbart

Conductive Anodonic Filament My worry is that any extra m... - Jan 04, 2010 by BoardHouse

BoardHouse

#60714

Water Washing | 21 December, 2009

Here is my question to the Guru's on this site.

Lead free boards to go though Wave / reflow - and then sent through a water wash 2 day's prior to Hand assembling a 50mil ribbon connector. This is a 4 layer board with 2x2116 pre-preg (.036 1/1 5x7628 core) construction .062 fin thickness.

Question:

1)Should their be any concerns regarding CAF 2)should the boards be baked before hand assembly is done 3)do they need to be baked at all prior or after hand assembly.

**These boards will be going through burn in electrical testing in 4-5 day's after hand assembly is completed.

My concern is that the water wash prior to hand assembly without baking out the moisture can open the door for CAF condition with the mix of Flux.

Please let me know your thought, Small assembly house is not sure if this process will be an issue.

Thanks for you input.

MLD

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cbart

#60761

Water Washing | 4 January, 2010

1) I'm not familiar with the acronym CAF. Could you spell that one out for me? 2)Why do you feel they need to be baked? Are they in a high humidity enviornment? the only time we bake is when we are dealing with moisture sensitive components. Do you bale the boards prior to Reflow and wave solder? if not no need to bake pre hand solder. 3) The rules we follow for baking pre-test is if the parts are susceptible to moisture entrapment and voltage is applied we bake out to remove any water which could create a short or cause impedance issues during test (we have found moisture to be an issue in RF applications).

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BoardHouse

#60763

Water Washing | 4 January, 2010

Conductive Anodonic Filament

My worry is that any extra moisture added to the Lead free Material during assembly may cause this Conductive filament to grow within the material weave. They are water washing after through hole assembly and then after water washing they are doing hand assembly.

I'm not so concerned about the water its self as I am thinking that it can open a channel for the flux to follow into the weave of the material itself to were as to start the CAF process or formation prior to Electrical testing or burn in of the finished assembly. Its this Electrical testing or burn in that has the potential to complete the puzzle by basically causing copper to migrate from hole to hole through the weave causing copper to plate across forming a high resistant short.

I have never seen this issue, but this process made me start to think that this could cause an issue.

I just get concerned when moisture is introduced into a lead free assembly prior to it being completely assembled,

Moisture and lead free Laminates are not friends.

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