Limiting PCB moisture absorption is the full responsibility of the supplier. How to pack boards right.
PCB suppliers who use good packaging methods are keeping their products safe from physical damage incurred during transit from the manufacturing facility to customers’ warehouses. Equally important, these packaging practices help ensure shelf-life expectancy by preventing moisture absorption.
To protect their orders, PCB buyers should require suppliers strictly follow corporate shipping specifications. Nothing is more frustrating than waiting for quality product to be built, only to have it damaged because of poor packaging practices. It’s just as frustrating when boards become useless while sitting on the shelf.
PCBs can be very heavy. Their sharp corners sometimes wreak havoc on the corrugated cardboard boxes in which they are shipped. A good freight spec should state boards are to be vacuum-packed with a bubble wrap base, with no more than 25 boards to a stack. When a board is oversized or heavier than normal, 10 to 15 pieces is the best option. Whatever number is used, the packaging should be consistent in count for a particular shipment.
Extra care should be taken for flexible or very thin, rigid PCBs less than 0.028" thick. They should be packaged with stiffening material on the top and bottom of the bundle to help prevent warping.
A humidity indication card (HIC) and desiccant are to be placed within the package as well. The HIC should be placed inside on top of the PCBs for easy review. The desiccant should be placed along the side or edge of the bundle, so it doesn’t contribute to bending or warping caused by the stress of the vacuum packaging.
Each PCB bundle should have a sticker affixed detailing the part number, date code and number of pieces per bundle. More than one date code of the same product may be shipped together if they are segregated and marked as such.
X’d-out panels, if allowed by your PCB fabrication specifications, should be packaged separately and clearly marked.
The individual packages of PCBs should be placed tightly in a box, with Styrofoam or other shock- absorbing material placed between the packages and the wall of the shipping container. The PCB corners should be protected, as they can be easily dinged or dented while in transit.
The weight of each box should not exceed 30 lb. Boxes may have exterior strapping applied when the PCBs are oversized or heavier than normal.
Each box should have a sticker on either end identifying its contents, including the part number, purchase order number, date code and number of pieces within the box.
Each part number shipped should come with a packing slip and “proof of quality” documentation, including (but not be limited to):
- The certificate of compliance
- A first article or dimensional report
- A microsection report to include a solderability test with a cross-section
- An electrical test report
- An ionic contamination report
- A TDR report (controlled impedance, when applicable)
- Any material certifications
- Any other documentation required by the purchase order.
When the product is shipped, the supplier should notify the customer’s purchasing, receiving and accounting departments of shipment method and tracking number. The commercial invoice and electronic copies of the quality paperwork should be included in case such documentation for the shipment is lost in transit.
As crucial as proper PCB packaging is, the storage of the boards once they reach the customer is just as vital. Other than opening one of the packages to verify the PCBs meet the criteria of the print and the documentation received, the best bet is to leave the boards in their original packaging.
A bare board begins to absorb moisture immediately upon leaving the factory. The amount of moisture absorbed depends on a variety of factors, including:
- Base material used in manufacturing
- Manufacturing environment
- Packaging method
- Shipping temperatures (from the cold bellies of aircraft or the humid transit of a sea shipment to hot delivery trucks)
- Customer storage and inventory procedures.
Vacuum sealing and the use of desiccant only delay or lessen moisture absorption. They do not prevent it.
The longer a PCB is stored on a shelf, the greater the chance it will absorb moisture, which can manifest in the assembly operation as delamination. Delamination is caused either by moisture or manufacturing defects. If a problem PCB is determined to be structurally sound, the cause most likely is moisture-related. A bake-out process before any additional assembly can remove most of the moisture, if not all of it. This permits the board to be assembled without issue.
IPC-1602, Standard for Printed Board Handling and Storage, provides suggestions for proper handling, packaging and storage of PCBs. It puts the full responsibility for PCB moisture content on the supplier, even after the finished product has left the manufacturing facility.
The way PCB suppliers package their products indicates their commitment to quality and reliability. It is the final step in the manufacturing process, and PCB buyers have a responsibility to ensure it is done right.
Greg Papandrew has more than 25 years’ experience selling PCBs directly for various fabricators and as founder of a leading distributor. He is cofounder of Better Board Buying (boardbuying.com); This email address is being protected from spambots. You need JavaScript enabled to view it..
