PCBA rework

I want just to confirm what Dave suggested you.

J-STD-033a, par 6. Boards Rework tells you plenty of useful informations. 6.1 Component removal, RWK and remount 6.1.1 Removal for Failure Analysi 6.1.2 Removal & Remount 6.2 Baking of Populated Boards

There you can find the way to do, but for sure You must know which kind of PCBA are you going to rework, thikness an layers, FR4, BT,etc, and which kind of components (MSD or not) you have to remove (how much local heating is necessary), etc, etc, so define if you really need to bake or not bake or just to do a simple PCBA preheat before rwk.

IPC-7711 and 7722 tells you the technique for rwk or repair, but they also recall precautions related to moisture sensitive components and PCB, so they ask to perform baking and preheaitng before to work on them. The value added comes with the engineer who is working on the problem.

By experience, what we do before to chose the bake cycle:

- check if any Electrolitic Capacitors are on the board (as you know they cannot withstnd above 105/115�C) - check if any LED are on the board - check if any MSD are on the board - check if any battery are on board (if yes we remove) - qty of layers (as you know moisture intrapped into PCB can cause delamination,internal plane separation, blistering,measling , etc when submitted to reflow temperature, or local reflow like for RWK, etc) - if we are in a HURRY or not !!!!! - etc

Then if not Electrolitic Caps or LED or battery,etc, the baking is driven by MSD next to where I have to rework on pcba, and thikness of PCB, so 125�C /24h is the choice (most of the case).

But if we are not in a hurry, we prefer a longer time and lower temperature, ie. 90�C/105�C 48h or more.

When Electrolityc Caps are on PCBA: 90�C 48-72 h or more When LED are on PBA :(if no eng tech data available)70�C, time could be 168-192 h.

PCBA pre-heat before large component (SMTs and BGAs)rework is another important step to take kare.

Any way if you are in the doubt, do not exagerate with temperature and leave your bords at 105�C for several days.

Regards

GLS

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