|Ask the Experts|
November 28, 2017
Bake for Repair
How much time is required to bake a mobile phone PCB assembly to eliminate the moisture inside, before doing any repair work on the components?
|Expert Panel Responses|
I would suggest you check the PCB bill of materials and base your bake time and temperature on the MOST moisture sensitive component on the board. If this information is not available you could bake the assembly for 24 hours.
Regional Sales Manager
OK International Inc.
Depending on the material of the PCB and the thickness, I would recommend a bake time on no more than 10 to 15 minutes.
Global Segment Manager
Air Products & Chemicals, Inc.
I suggest you refer to IPC/JEDEC J-STD-033B.1. Table 4-1 of this industry standard provides reference conditions for drying moisture sensitive devices (MSDs) that have exceeded their allowable exposure time. This table is applicable to both unmounted and mounted MSDs. A bake temp of 90C is usually recommended for drying the MSDs already mounted on a PCBA, prior to rework. The higher bake temp of 125C is NOT generally recommended for PCB Assemblies, because the plastic shrouds on common headers & connectors (which may have been added post-reflow), cannot withstand long-term exposure to 125C. The required bake duration at 90C ranges from 11 hours to 10 days, depending on the following 3 variables: 1) Moisture Sensitivity Level (MSL) of the MSD(s) on the board. 2) MSD Package Body Thickness 3) Elapsed time since expiration of Floor Life of MSDs on the PCBA. If this is unknown, then the safe bet is to use the column entitled "Exceeding Floor Life > 72 hours". Based on the above 3 variables, Table 4-1 provides all the information your readers need to ensure MSDs on PCB Assemblies can be sufficiently dried, to survive thermal excursions during rework and repair operations.
Sales Manager (Americas)
Unfortunately, there isn't a simple answer to your question. Let's take a detailed view of your inquiry.
Director of Engineering
Innovative Drying Co.
Definitely you have few variables on this problem statement - how much time the board was out for, what is the material spec, what is the population type on the board, board thickness, etc. For the PCB itself the supplier is the one that can give you the exact specs and recommendations for the baking process. However when you perform the baking I recommend a vacuum bake - this will allow you to use below water boiling point temperature to dry the moisture out.
Engineering and Operations Management
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