Board Buying
Shortsighted approaches lead to overspending.
Most air freight – including for printed circuit boards – is hauled in the cargo holds of passenger aircraft. While the number of available flights is slowly increasing as Covid restrictions lessen, the price is still high, and getting PCBs delivered on time and at a reasonable cost remains a significant challenge for buyers.
That’s why they should negotiate with suppliers for a “delivered” price.
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.
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); greg@directpcb.com.
Just like housing, a little extra size can cost a lot more.
Printed circuit boards in panel or array format increase the efficiency of the assembly operation, especially in volume applications. Takt time is greatly reduced, and handling of product is easier. However, rising material prices are cutting into that advantage because more material is required to produce those arrays.
PCB costs are based on the amount of raw material required to make a particular board. The metal finish, like ENIG or silver, plays a part in pricing, but it is the amount of fiberglass and copper needed that really determines the final cost.
The quoted price for most boards in panel or array format is based on a fabricator's desired panel price for a particular technology or quantity, divided by the number of arrays (or pieces) that fit on a standard 18 x 24" manufacturing panel. The more arrays or pieces that fit on the panel, the lower the cost.
Whether that price is dictated by the number of boards (arrays) that can fit on the standard manufacturing panel, or by the total square inches of the finished array, a quarter or half-inch too long in one direction may mean a double-digit price difference.
Review pricing with current and outside suppliers to confirm you are paying the going rate.
“We don’t have the bandwidth to move business.”
That's what a printed circuit board buyer told me recently.
Let’s unpack that because it could be a shortsighted attitude.
When an EMS firm puts a PCB supplier on its AVL, it often asks only for pricing on new projects. When it comes to existing work, the response is often, “We don’t move boards once they are placed,” or, “we don’t have time to rebid those,” or, “it takes too much effort to move to another vendor.”
Even in the face of rising board costs, many buyers and procurement managers resist moving production away from suppliers they’ve used for years.
Buy PCBs with your brain, not your heart.
“Pray for me. I buy circuit boards.”
That was a saying posted on the wall of a prospect I visited some 25 years ago. It’s funny, of course, but it also speaks to an unchanging truth about PCB buying: It’s often an emotional experience, especially when it comes to the bare board.
The PCB is the foundation of your products. It represents a good chunk – about 8 to 12% – of the cost of the bill of materials. While it is the first item needed to begin the assembly, it is usually the last item ordered. That alone can make buying boards stressful.
In my years selling boards and training companies how to buy PCBs, I’ve found it’s not a lack of knowledge about circuit boards that prevents buyers from leveraging their annual spend most efficiently; it’s misplaced loyalty or an aversion to risk.
A board’s level of technology should dictate how often to expect imperfections.
One of the most common questions I get from PCB buyers is, “How many X-outs are acceptable?” Some might say receipt of a PCB manufacturing panel or array with any X-outs indicates the supplier cannot maintain a high level of quality.
This is not necessarily the case.
An X-out occurs when a defective board in an array or manufacturing panel of like PCBs has been shipped. The board is literally marked with an X in permanent marker to signify it is flawed.
While a panel or array with zero X-outs is ideal, the board’s level of technology should dictate how often to expect this kind of perfection. If the board is a single-, double- or easy four-layer item, then a PCB buyer should expect – in fact, should demand – the manufacturer deliver panels free of defective boards.
However, if it is a higher technology – such as an HDI design – scrap will happen in every manufacturing lot. To expect otherwise is not realistic.
Any experienced PCB supplier knows this custom-made item – requiring more than 100 different manufacturing processes – will have a board (or boards) with some sort of rejectable imperfection in every manufacturing lot released to the floor. To address this issue, before the board order hits the production floor, the fabricator will release an overage, depending on the board’s technology, to ensure its manufacturing processes yield the number of boards required to fulfill an order.
The more high-tech the board is, the more overage may be necessary to account for any fallout.
For example, let’s say 1,050 pieces are released to meet an order requiring 1,000 individual boards. In this case, the manufacturer decides a board’s technology will require only an additional 5% in materials overage.
At final QC, the vendor then finds 32 pieces (or about 3%) did not make it through the manufacturing process for various reasons. Those bad boards are scrapped.
Because a 5% overage was produced, 1,018 pieces are good. So, the 1,000-piece order is shipped as promised, and the additional 18 pieces are put into finished spares. Everyone is happy, with most customers not paying any attention to the fallout that occurred within that overage amount.
Sometimes, though, having PCBs delivered in an array or panel format might highlight manufacturing challenges, especially when a customer has a “No X-out” policy.
If you put that same order in a four-up array, then 250 arrays would need to be perfect to meet the 1,000-piece requirement. Based on those numbers for that technology, the manufacturer could expect the same percentage of fallout. But boards found at final QC that don’t pass muster are “connected” to three pieces that passed with flying colors. This means 32 arrays with an X-out or 128 pieces total (32 x four-up) are not allowed to ship, regardless of their quality.
The vendor must release more overage (about 15%, or 152 pieces, because it’s a four-up array) to accommodate the normal fallout that occurs during the manufacturing process for arrays that can’t have any X-outs.
Whether your company accepts X-outs or not should be detailed in your firm’s PCB fabrication specifications. This information will guide your board suppliers on how much material (overage) they must release – based on their technical capabilities – to fulfill an order.
Here is an example of an EMS company’s X-out policy that is clearly spelled out:
“X-outs are allowed. However, not more than 20% of the PCBs in the array can be X’d-out, and no more than 10% of the arrays to be shipped may contain an X-out.”
This means if you have, say, a 2,000-piece order manufactured in a 10-up panel requiring 200 arrays to be received, the most you should receive is 20 panels that contain no more than two X-outs each.
Your fabrication specs should also state how X’d-out panels are to be received to avoid causing headaches for both receiving and production departments. A statement like this works:
“X’d-out arrays are to be segregated and identified accordingly at time of shipment.”
PCB buyers should keep in mind the amount of real estate needed for perfect arrays (no X-outs) means the overall cost of the board will be higher. The adage about not allowing the perfect to become the enemy of the good is applicable here.
Before your company sets its X-out policy, sit down with your manufacturing department. There are ways for an assembler to handle manufacturing panels with X-outs, but the department responsible for shipping quality, finished assemblies should have final say on X-outs.
A rigid “No X-out” policy will likely cost you more without improving the PCB manufacturing process. In most cases, a more flexible approach is warranted.
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); greg@boardbuying.com.
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