Safe And efficient PCB drying accomplished with no damage to higher temperature ranges using extremely reduced moisture drying enclosures to produce an atmosphere that contains less than .05g/m3 water vapour.
Guidelines for the appropriate stocking and moisture safety of Dry Storage Cabinets can be found in IPC specifications (IPC-J-STD-033C). Since there had been no released standards for storage space and dampness protection for printed circuit boards till 2010, (IPC 1601) they were typically overlooked. But with the right stocking manage and the usage of professional drying out methods, considerable advantages may be gained: Coated printed panels will stay solderable to get a much longer time and harm throughout reflow due to dampness could be removed.
The ‘IPC-1601 printed table dealing with and storage guidelines’ claims that “ If procedure controls are ineffective, and printed boards have soaked up excessive moisture, cooking is regarded as the practical remedy.” It goes onto state, “However, baking not merely increases cost and cycle time, additionally, it may degrade solderability of the printed table which requires additional dealing with and increases the probability of dealing with damage or toxic contamination. In general, both printed table fabricator and also the consumer ought to make an effort to avoid cooking by exercising efficient handling, packaging, storage, and process controls…”
The document also claims “Baking will not be appropriate for OSP films, because it deteriorates the OSP complete. If cooking is considered necessary, the usage of the lowest feasible temperature and dwell time is advised as being a starting place.”
Natural solderability preservative (OSP) coatings are probably the top surface area finish options in lead free soldering simply because they provide an appealing blend of solderability, simplicity of processing and low cost. When compared with alternatives, however, they tend to be probably the most prone to oxidation. The reason for this particular is based on the pure copper surface area protected only by the OSP coating layer. Below normal climatic conditions in a production procedure, right after only a few minutes you will have a splitting up of a water film on the surface (3-5 atom levels). This then starts a diffusion procedure which results in a vapor stress equilibrium from the OSP coat.
Cooking also speeds up strong diffusion among metals, and raises intermetallic growth. This might lead to a “weak knee” or other solderability problems if the intermetallic layer gets to the outer lining and oxidizes.
The packaging quality of PCBs as received from your manufacturers can also have a substantial effect. Often a easy foil handbag or even an ESD handbag can be used rather than a Moisture Buffer Handbag (MBB). With such packaging coated boards are likely to arrive getting currently soaked up moisture, and if kept like this they are useless following a short time. Adsorption process Electronic Dry Cabinets can be used the careful drying out of these and other moisture delicate gadgets.
In addition to extending safe storage space time, defects and damage (demonstrated previously mentioned), like popcorning and delamination throughout reflow may be prevented with appropriate dealing with and storage.
Safe and efficient PCB drying can be achieved without damaging higher temperatures utilizing extremely reduced humidity drying enclosures that create an atmosphere that contains lower than .05g/m3 water vapour. This produces a ‘moisture vacuum’ that releases the previously soaked up moisture from your PCBs while safeguarding towards oxidation and inter-metal development. These enclosures will also be appropriate for safe storage of PCBs for unlimited occasions, per IPC/JEDEC specifications. Further oxidation is stopped by the removing of the electrolytic water molecules. Since these storage space techniques could work at space temperature, boards will not need to be eliminated until prepared for processing. Reduced temperature heat can be used to accelerate the drying time. (See reference conditions for drying below).
Dried and kept this way the OSP covered published board is preferably protected and may be used over long time periods with constant wetting qualities.
Dry storage space can also be required for a less critical coating; e.g. initially the wettability in the covering of any heat tin-plated published table is better than of OSP coated printed panels. Here an oxide movie forms at first glance intoxicated by dampness impact which can also restrict great wetting and solderability. This challenge can be averted through the help of a dry cabinet, allowing the preservation of any continuous wettability for a considerably longer time period.
The recommended drying occasions were determined as outlined by IPC-STANDARD JSTD 033C for drying out of elements. Simply because variation in accordance with MSL-Level from your PCB-producers is not really yet contained in the regular, measures were performed on check boards. These showed, that the MSL-Level 3 of components is comparable using the behavior of Dehumidifying Dry Cabinets.
Exceptions are for PCB’s with lots of surface area layers and copper division inside, the density in which must be multiplied with a factor 2 beforehand. As these levels may have a strong impact on the speed of dehumidification, these specs needs to be searched upon as guidelines. Because of the complexity of influences, a precise judgement is anmtvj feasible using a PCB-particular dehumidification test.