PCB Baking after Wash

Hi System Steve,

What is a solvent cleaner over water wash? Solvent first and then rinse with water? And why do they feel the need to bake the boards? Do they think trapped moisture will cause board damage?

reply »

Hi Steven,

The 24 hrs bake is an overkill according with various J-STDs. Assuming a bake temperature over the 100 Celsius degrees.

There are several factors to be considered before deciding the best methodology to wash misprinted board. However, there is no enough information in your previous message to formulate a recommendation.

However, you can contact me by email: maacolomer@yahoo.com or call me at 813-476-0755 to talk about the differents factors to be considered.

Thanks, M. Colomer, CSMTPE

reply »

Dear Steven:

Often the recommendations for baking prior to assembly are derived from various J-stds. But J's currently concern baking moisture out of components, and fail to address the moisture issues of the PCB. Because of that, there is the IPC D-35 committee, of which I am a member. We're in our 4th year working to develop the IPC-1601, Storage and Handling standard, which intends to engage the whole of the electronic assembly (rather than selective componentry) in practices that will mitigate the effects of increasing thermal shock and latent moisture. The opportunity for the PCB to absorb moisture after wash-down is a given. How much moisture is a variable based on the PCB's type of exposure (spray vs. immersion) the kind of moisture (cleaners vs. water) time & temperature of the liquid and the type of substrate being exposed (hygroscopic properties are a variable). The consequence of latent moisture in the PCB can lead to delamination, a separation of the layers (or prepreg plies). These can appear and range from minute bubbles thru coin-sized blisters. The failure mechanism is simple: If the rate of trapped moisture expanding during a subsequent thermal pass exceeds the laminate's bonding agent strength, the bond fails and delamination begins. What the "old-timers" know is that a slow low[er] temp. pre-bake is good insurance against reflow or wave-shock delamination. eMail me if you're interested more on this subject, and I'll be glad to provide more from the PCB perspective.

reply »