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PCB storage for lead Free

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MM

#56522

PCB storage for lead Free | 16 September, 2008

Can anyone tell me if there is a procedure for storing raw PCB's? We currently are seeing an issue with lead free boards with dewetting. We tracked it down to one or two datecodes, but not all of the boards have dewetting. Is there a expiration date on lead free pcbs or what are others doing to prevent contamination? I ran a test with a solder sample with dewetting and sprayed half of the board with a stronger flux and ran it through the oven. Results of the board that was sprayed had no dewetting problem. Any suggestions are greatly appreciated.

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#56547

PCB storage for lead Free | 16 September, 2008

Q1. Can anyone tell me if there is a procedure for storing raw PCB's? A1. Yes, there are thousands of procedures for storing raw PCB. Why so many? Everyone writes their own procedure. Generally, they say: * Boards require individual separation and protection to prevent damage using antistatic plastic wrap and sealed * Environmental controls for storage: 50% RH, 65-75F

When you view fabricator sites, they blab-on about this finish and that finish lasting in storage for this many months or that many months under "Optimal Storage Conditions." We've found only one that describes what they consider "Optimal Storage Conditions." The rest just pretend they're not expected to describe "Optimal Storage Conditions" after they bring it up in their discussion. Fascinating.

There are standards but ... * IPC-6011, 5.0 Preparation For Delivery, 5.1 Packaging. Printed boards shall be packed in accordance with minimum packaging which will afford adequate protection against corrosion, deterioration, and physical damage during shipment from the supply source to the first destination. Methods of packaging shall be determined by user requirements. * IPC-1601 Printed Board Handling And Storage Guidelines, Strawman Draft, March 31, 2008 has outlines for sections on bare and assembled board storage. Look here: http://members.ipc.org/committee/drafts/D-35_d_1601Strawman.pdf

* MIL-PRF-31032, 1 November 1995, 5 PACKAGING, 5.1 Packaging requirements. The requirements for packaging shall be as specified in the printed board procurement documentation.

Q2. We currently are seeing an issue with lead free boards with dewetting. A2. Is this what your �dewetting� looks like: http://www.bobwillis.co.uk/defect_browser/pages/04.htm

Generally, dewetting is not something that you can fix with more active flux. Would you attach pix?

Q3. Is there a expiration date on lead free pcbs? A3. No. There are many different formulations of materials for solderability protection. Each has different properties. [You can find tables comparing these properties on the web.] This is compounded by the fact that, while there are guidelines on the shelf life of each of these materials, supplier fabrication methods and material remain major drivers to shelf life. Specifically, what is the solderability protection on your boards?

Q4. What are others doing to prevent contamination? A4. What is the contamination on your boards? Generally, contamination does not cause dewetting. That your board solders with a more active flux indicates that there may be a contaminant on your board.

Any suggestions are greatly appreciated ... Use the more active flux

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Reflow Oven