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PCB SHELF LIFE AFTER FIRST REFLOW

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#73465

PCB SHELF LIFE AFTER FIRST REFLOW | 9 February, 2015

What is the maximum PCB shelf life for double side PCBs after first reflow? I mean, after assembly bottom side, how long can I keep the PCB without solder paste waiting for the second reflow? (Considering exposure on production environment conditions) I didn't find any recommendation on IPC or Jedec documents.

Regards

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JAX

#73466

PCB SHELF LIFE AFTER FIRST REFLOW | 9 February, 2015

Without knowing the surface finish of the PCB lets focus on an alternative problem... At a minimum, you need to look at the 1/2 built assembly like individual components, all having their own MSD levels and all subject to 2nd side reflow temperatures without having the opportunity of having the moisture removed...

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#73467

PCB SHELF LIFE AFTER FIRST REFLOW | 9 February, 2015

In my case most of the PCBs are OSP finishing and worst case of MSD component on bottom side is level 3 (168 hours). You mean that PCB shelf life with bottom side assembled shoud be 84 hours?

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JAX

#73468

PCB SHELF LIFE AFTER FIRST REFLOW | 9 February, 2015

Outside the MSD issues stated already (and I cannot provide a exact time not knowing multiple factors like Humidity levels, temps, exposure times, etc...)

OSP might be the very worst finish to use in this scenario of side 1 / store on a shelf / side 2

Do you pre-bake the boards before assembling the first side? This could degrade the protective coating.

Do you wash the boards after assembling the first side? If you wash using alcohol or solvents, the coating could degrade... this would also happen when you clean misprints during the build process.

How many heat cycles will this product see before completion? Each one will degrade the finish.

Overall... if you have determined that the PCBs and Components can take the second heat cycle and not be damaged by MSD related issues, your only concern is solderability... and that is easy to check.

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#73469

PCB SHELF LIFE AFTER FIRST REFLOW | 9 February, 2015

Thanks for the support Jax. Our current scenario:

Baking - Not allowed for PCBs

Washing - Not allowed

Heat Cycles - 2 (Bottom and top side). It's a notebook board

Our concern is related to solderability because OSP finishing will be seriously impacted after 1st reflow. Usually we do not exceed 5 hours between bot and top side but we are trying to figure out the correct exposure time based on IPC/Jedec.

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JAX

#73470

PCB SHELF LIFE AFTER FIRST REFLOW | 9 February, 2015

If solderability is the only concern, then there is no standard time. Multiple factors involving OSP thickness, Flux activation levels, profile parameters, storage environment will drive the problem. You just need to perform tests to determine your maximum exposure limit for your own process.

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