To Bake or Not to Bake (in Rework)—That is the Question


Reading time ( words)

When performing rework on printed circuit boards, the issue of the moisture having to be baked out of the PCB is often debated. Whether it is localized mini-wave rework, hand-soldering or convection rework, the board, as well as neighboring components, needs to be taken into account in terms of moisture protection during the reflow cycle. The board components’ protection of moisture ingress and subsequent part “popcorning” or heat damage is governed by the IPC-J-STD-033 Handling, Packing, Shipping and Use of Moisture/Reflow Sensitive Surface Mount Devices, whereas the board moisture ingress and its potential measling or delamination is governed by the IPC-1601 PCB Handling and Storage Guidelines. Along with the components mounted to the PCB, in some cases, the boards need to be considered as MSD devices.

In the case of PCB rework, the component to be removed is typically going to be discarded, which means there is no concern with the removed part having moisture damage. If the device is to be removed and sent back for further failure analysis, then baking of the board/parts is recommended. If you look at the rework guidelines from TI, Kyocera, Intel and other major component vendors, you will find that they recommend to bake the boards and parts prior to another reflow. In addition, care must be taken to make sure that parts that are temperature-sensitive, such as batteries, capacitors, plastic connectors and under filled or glued components, may need to be removed or protected correctly.

As part of the process the board rework areas should be properly masked and shielded so that the components are protected from reflow temperatures. There are a variety of materials that can serve to protect neighboring devices in order to make sure they remain unharmed during the rework process both from a parts removal and replacement standpoint. Shielding of the components so that they remain undamaged by localized reflow temperatures may be necessary depending upon their proximity to the reflow location. Other reflow sources or complete part removal are other strategies that will protect the components from thermal damage or MSD exposure.

After baking is complete, make sure to properly tag and mark the board or parts such that the exposure history can be documented. Place these components or boards into a dry environment such as a dry box in order to house the parts or boards prior to being exposed to the environment again. An alternative is to place them in a moisture barrier bag, and putting desiccant and a moisture indicator card on the inside prior to sealing in order to have solid MSD controls in place.

Read The Full Article Here

Editor's Note: This article originally appeared in the June 2016 issue of SMT Magazine.

Share



Warning: array_rand(): Second argument has to be between 1 and the number of elements in the array in /home/iconnect/releases/20160311/public_html/elements/next_item.php on line 41

Suggested Items

The Year of IoT Digitalization

12/15/2017 | Michael Ford, Aegis Software Corp.
There is no longer any significant disagreement that having an industry-wide standard for IoT communication is absolutely essential for digitalization of factories if they are going to deliver on Industry 4.0 performance expectations. Digitalization of manufacturing is the key business opportunity of the decade, whoever and wherever you are, so stand-up and be a part of it, and create your opportunities.

Solder Printing Process Inputs Impacting Distribution of Paste Volume

12/14/2017 | Marco Lajoie and Alain Breton, C-MAC Microelectronics
The volume of solder deposition, like any process, has variations that may be characterized by a statistical distribution curve, whether normal or non-normal. As complexity, density, cost and reliability requirements increase, there may be value in narrowing the distribution curve. It is common sense that less variation serves the interest of quality of the more complex and dense circuit boards.

Tips & Tricks: Generating Stencil Tooling

12/13/2017 | Ken Horky, Peterson Manufacturing
Many engineers are leaving the editing up to the stencil fabricator these days. From the outside, this may appear as a time saver for process engineers, but considering how many stencil redos have been required and how many processes that have run 'sort of OK,' there's a tremendous amount of scrap and rework that could be saved from just a little more attention paid to stencil tooling.



Copyright © 2017 I-Connect007. All rights reserved.