Safe And effective PCB drying accomplished without damaging high temperature ranges utilizing ultra reduced humidity drying enclosures to produce an environment containing less than .05g/m3 water vapour.
Guidelines for that appropriate stocking and dampness safety of Low Humidity Cabinets can be found in IPC specifications (IPC-J-STD-033C). Since there were no published specifications for storage and dampness safety for printed circuit panels till 2010, (IPC 1601) they were generally ignored. However with the right stocking manage and the use of expert drying methods, considerable advantages may be acquired: Covered published boards will remain solderable for a considerably longer some time and harm throughout reflow as a result of moisture may be eliminated.
The ‘IPC-1601 printed board handling and storage space guidelines’ claims that “ If procedure controls are ineffective, and published boards have absorbed extreme moisture, cooking is the most sensible treatment.” It is going on to state, “However, baking not only increases price and period time, it can also degrade solderability from the published board which requires extra dealing with and boosts the probability of handling damage or contamination. Generally, both printed table fabricator and also the consumer should make an effort to avoid cooking by exercising efficient dealing with, packaging, storage, and process controls…”
The document also states “Baking is not really suitable for OSP films, because it deteriorates the OSP complete. If baking is considered essential, the usage of the cheapest possible heat and dwell time is advised as a starting place.”
Organic solderability preservative (OSP) coatings are among the top surface finish options in lead free soldering because they provide an attractive combination of solderability, simplicity of processing and low cost. In comparison to alternatives, nevertheless, they are usually probably the most vulnerable to oxidation. The main cause with this lies in the pure copper surface area protected only by the OSP coating coating. Under typical weather problems inside a manufacturing procedure, right after just a few minutes you will have a splitting up of a water film on the surface (3-5 atom layers). This then starts a diffusion process which results in a vapor stress balance with the OSP jacket.
Baking also accelerates solid diffusion between precious metals, and raises intermetallic development. This may lead to a “weak knee” or some other solderability problems in the event the intermetallic coating reaches the outer lining and oxidizes.
The packaging quality of PCBs as obtained through the producers can furthermore have a significant impact. Normally a simple foil bag or even an ESD handbag is used rather than a Moisture Buffer Bag (MBB). With your packing covered boards are likely to arrive having currently absorbed dampness, and when kept like this they will be useless following a limited time. Adsorption procedure Electronic Dry Cabinets can be used for the careful drying of these and other dampness delicate devices.
As well as extending safe storage space time, problems and damage (demonstrated above), like popcorning and delamination during reflow may be avoided with appropriate dealing with and storage.
Safe and effective PCB drying out can be accomplished with no damage to higher temperature ranges utilizing extremely reduced moisture drying enclosures that create an environment that contains lower than .05g/m3 water vapor. This produces a ‘moisture vacuum’ that releases the formerly absorbed moisture through the PCBs while protecting against oxidation and inter-metallic growth. These enclosures can also be appropriate for safe storage space of PCBs for unlimited times, for each IPC/JEDEC specifications. Further oxidation is stopped by the removal of the electrolytic water substances. Because these storage space systems can work at space temperature, panels do not need to be eliminated until ready for handling. Low heat heat may be used to speed up the drying time. (See guide conditions for drying below).
Dried out and kept in this manner the OSP covered printed table is preferably safeguarded and can be utilized more than long time periods with constant wetting qualities.
Dried out storage space can also be essential for a much less essential coating; e.g. at first the wettability from the covering of the heat tin-plated published board is preferable to of OSP covered printed panels. Here an oxide movie forms on the surface under the influence of dampness impact which can also limit great wetting and solderability. This problem can be averted with the aid of a dried out cupboard, enabling the preservation of a continuous wettability for any a lot longer period of time.
The recommended drying out times had been decided as outlined by IPC-Regular JSTD 033C for drying out of elements. Simply because distinction as outlined by MSL-Level from your PCB-producers is not really but within the standard, steps had been completed on test boards. These showed, that this MSL-Degree 3 of elements is similar using the actions of Desiccant Dry Cabinets.
Exclusions are for PCB’s with lots of surface layers and copper department within, the thickness of which should be increased by a aspect 2 in advance. Since these layers could have a strong effect on the speed of dehumidification, these specs needs to be looked upon as recommendations. Because of the complexity of influences, a precise judgement is anmtvj feasible using a PCB-particular dehumidification test.