Complicated issues tend to be long-lasting. The question of “x-outs” is one. Simply explained, x-outs are rejected, but marked printed circuit boards on a assembly panel when it is delivered to the subcontractor. Of course, you do not pay for these PCB´s, but they can cause problems and extra work at some subcontractors. Thats way many do not allow panels that include x-outs. As an established supplier, and former manufacturer of printed circuit boards, it is something that we have many times been reflected on. Here we give our view on the matter and with it perhaps also startup a constructive debate.
DISADVANTAGES OF X-OUTS:
Assembly machines does not support x-outs
Some Pick-and-place machines do not handle x-outs and require separate programming for each panel containing x-outs. Over the years, this has slowly become a minor problem, however many see an extra work with the general handling of the x-outs.
Sorting and handling
There will be a separate handling of the panels that contain x-outs. Often packaged in separate vacuum packs. Unfortunately, some factories do not do this. And causes therefore the extra step of sorting the panels.
Nearby PCB´s may be on the verge of failing
This can be considered the heaviest argument. There is definitely a reasonableness in this. However, we must take into account WHAT is the reason why the PCB was rejected. Is there an error resulting from a process that can affect the panel in general? For example, if the error is due to too low hole plating, it can be assumed that the hole plating is doubtful on the whole panel. However, if a fingerprint that made the surface treatment unusable on one PCB, does not mean automatically that nearby PCB´s have the same error. Even less all the PCB´s on the panel.
Higher freight cost
X-outs on the array panel are not charged and the total number of ordered PCB´s is still delivered. Which means that producer have to ship the failed PCB,s to the customer, who pays for the freights total weight. At least in theory, it will then be a higher freight cost. Of course depending on whether the shipping is included in the PCB price or not.
The way to mark x-out can affect further production
This has long been a difficult nut to crack. There is no easy and sustainable system to mark x-out´s that do not create other problems. The most common, is to simply mark with a cross on the PCB´s that are rejected, with a permanent marker. Unfortunately, sometimes some marker can dissolve in flux or lacquer and cause damage to adjacent PCB´s. There are also small self-adhesive patches to mark x-out´s, but these can fell off and cause problems. An unusual, but bad method is thet the PCB factory drill a large hole in the rejected PCB. However this is the worst method, as the solder paste lands in the hole and smudges during printing. A really resistant marker is so far the least bad alternative to mark x-outs.
ADVANTAGES OF ALLOWING X-OUTS:
Cheaper PCB´s
Standard PCB´s which are relatively large and are few per assembly panel is rarely more expensive if “no x-outs” are required, but if there are more PCB´s per panel, and if they are more advanced, it can cost from 10% and up for “no x-outs” requirement. If you go even further and have large panels with really small, and advanced PCB´s, it happens that the manufacturer wants to double the price. Or even dare not to manufacture it at all. This is because the risk is so high that there will be at least one x-out on the panel.
More environmental friendly
The printed circuit board factory always produce a so-called overproduction of the ordered quantity. This to cover unforeseen losses during production. It is very rare that this overproduction comes for use and are usually discarded. If x-outs are not allowed, the manufacturer must take this into account to have a higher overproduction which is then wasted.
Or even worse:
Let’s say we have an order of 500 pcs. and “x-outs” are not allowed, and there are 50 pcs. per panel. When the factory finishes production, it turns out that there is one failing PCB on every panel. Then they are forced to reject all 500 PCB´s. Of which 10 pcs. are incorrect and remaining 490 pcs. fully functional.
Consensus: The manufacturer is not forced to reject fully functional printed circuit boards if x-outs are allowed.
Avoid the risk of getting “transplanted” PCB´s
A slightly but not completely insignificant risk you may take if you do not allow x-outs, is that you can get so-called transplanted PCB´s on a array panel. It means that the manufacturer breaks out a rejected PCB and replace it with an approved one from another panel. Often this is quite sloppy done and are often glued to the breakpoints, witch result in a poor location precision of the single PCB. Today, however, there are advanced tools and machines today, which are used to preform a more sophisticated replacement of the rejected PCB, by the way of CNC technology. However, Multi-Teknik´’s general rules do not accept transplanted PCB´s in any form.
The human factor
We are many who work in the process industry and know how difficult it is sometimes to interpret requirements and regulations. Especially when it comes to inaccuracies that do not have a definite form, appearance or if there is no clear boundary between “passed or failed”. If it depends on whether a single PCB is “good or bad”, and the manufacturer must make a decision about scrapping the batch and reproduce it over again, we want to say that there is a natural tendency to pass. Not because producer are deliberately breaking rules, but because its human.
CONCLUSION
How to reason then? A good idea is to first look at your own ability to handle x-outs. Do you have machines and software that handle x-outs? Do you have routines for sorting and handling x-outs? Maybe there is room for improvement here? A compromise can be that you actively choose for which part number you can accept x-outs. Small complicated PCB´s can be very expensive on a large array panel, and another PCB do not get more expensive at all. Another thing to consider is the percentage of x-outs you can reasonably handle in a batch.
We at Multi-Teknik of course deliver the PCB´s according to the requirements you set. If you order without x-outs, we deliver without x-outs. Our internal and general requirements for printed circuit boards where the customer does not have stated requirements for x-outs, is a maximum of 25% x-outs per panel and a maximum of 3% of the panels. As well as separately packaged. In addition to this, we do not allow panels with x-outs that may result from any general process (ex. a chemical) ,as there may be a theoretical risk that nearby PCB´s on the panel may be affected.
No matter how you turn this around, we all have an obligation to our environment and ours industry as a whole, to sensibly review how we consider to allow x-outs or not. Is it reasonable to throw away tons of fully approved printed circuit boards? Even if it most often occurs in other parts of the world.
