The Ten Commandments Of Packaging

Semiconductor packaging continues to evolve as chipmakers find new ways to fit more functionality into smaller spaces. Whereas the package once served primarily as a means of attaching a chip to a circuit board and protecting it from damage due to heat, moisture, etc., packaging today plays an important role in adding value to the device, boosting customization while helping to reduce costs.

In my 36 years as a packaging engineer, I have learned some truisms about packaging that are important to bear in mind as we continue along the path of new packaging technologies. My Ten Commandments of Packaging, while not an exhaustive list, highlights some things of particular importance in today’s environment, where many more complex package types abound. Even if these are not new to you, they bear repeating.

1. Reduce/minimize handling. Excessive handling in chipmaking, whether of the wafer, chip, package, or materials, creates mechanical damage (e.g., chipping and cracking) and electrical damage (e.g., damage from electrostatic discharge, which is hard to pinpoint, so it’s best to avoid it in the first place). A universal tray can be key because regardless of package size, you can put different slots inside the tray for ease of opening and closing. This allows you to have one tray or carrier with different slots for multiple part sizes. Full automation – where parts are utilized from built-in input/output trays, put in and go through all the necessary processes with minimal human interaction/touch — is the ideal goal, as it eliminates the opportunity for damage, contamination or breakage. However, automation is a costly approach often requiring custom tooling, which makes universal trays an ideal interim solution.

2. Cleanliness is super critical. The term “bug” was first used by computer pioneer Grace Hopper, who publicized the cause of a malfunction in an early electromechanical computer. She noted that operators, having traced an error in the Mark II to a moth trapped in a relay, carefully removed it and taped it to the logbook; from then on, “bug” became a computer term. The point is that cleanliness is a top concern, particularly with chip-on-board (COB) technology, where the silicon is exposed. In our business, we handle a lot of silicon, so optimal cleanliness must be maintained consistently; this makes continuous cleaning of the air especially vital. Organic materials (such as dead skin or fingerprints) will carbonize at high temperature. Carbon is conductive; if it lands in the wrong spot on a chip, it will create a short. Therefore, you must establish stringent cleanroom protocols and ensure they’re followed.

3. If you see something, say something. Sometimes, operators spot something they consider problematic, but they may be reluctant to stop the process, as they don’t want to incur downtime, inconvenience people, or negatively impact customers’ schedules. But a problem ignored can become a problem magnified – it’s important to establish an environment where speaking up is encouraged. For example, implement an employee incentive program that offers rewards tied to continuous process improvement (CPI). Addressing a problem and providing a solution while it’s small saves time and money in the long run, ultimately streamlining the packaging process.

4. Predict failures. To avoid future failures, you need a mechanism for anticipating them and preventing them from occurring in the first place. Say you go home one rainy day and see water dripping from your ceiling — clearly, you have a leaky roof. If you do nothing, it will only get worse, and pretty soon you’ll have a very costly repair on your hands. You have to fix the problem as soon as you see the drip. This concept applies to the packaging process, too. When we’re printing ink onto a ceramic, the smallest intrusion, or contamination that creates an intrusion during the printing process, can cause a crack once you start laminating. Implementing predictive measures can create some waste, but a small amount early in the process is far better than a lot later on.

5. Mitigate environmental effects. Electrostatic discharge (ESD) is a huge problem on a chip. Simply put, when two materials come in contact, it creates a buildup of static, and if there is no path for the current to flow through, the combination of high voltage and low current flow can and will damage the silicon. These damages become an even greater threat when more exotic materials are involved. Yet, the problem can be difficult to pinpoint — the damage may happen in a very small space that can only be spotted on a scanning electron microscope (SEM) image. Relative humidity (RH) is also a variable that requires tight control (35<RH<65%). If too high, RH can create moisture damage such as tool corrosion, but too low an RH can exacerbate ESD and will require shutdown of the line until a humidifier can be put in place. In addition to an efficient AC system, wrist/foot straps and other external tools, packages must integrate ESD protection.

6. Verify your own work. Before moving parts on to the next process step, every technician or engineer should double-check his/her own work to make sure it’s complete, and that it’s properly prepared for the subsequent process to avoid creating any bottlenecks. For example, if you are performing die attach, be careful not to create a bump underneath the die that will skew the die and create issues with wirebonding. Understanding all the different steps, not just your own, helps ensure that you’ll be completing your step with the next one(s) in mind.

7. Check each other’s work. This is the logical follow-on to the step above — don’t only cross-train, but cross-check. For example, if your step is to make a traveler for the package and another team member alerts you to a mistake you made but didn’t catch, congratulate the other person for their sharp eye. Do not take it personally or make an issue out of it — always bear in mind that the focus should be on what’s best for the customer. The goal is to avoid problems so that everyone’s efforts pay off by succeeding for the customer.

8. The devil is in the details. Pay attention to every detail, no matter how small it seems; those are the ones that can trip you up. In my career, I’ve seen that little things can have a severe impact on virtually any aspect of the packaging cycle, be it quality control, engineering, sales, you name it. A small error in printing that isn’t caught in proofreading can be disastrous. This is why it’s also important to document how to perform each step or process so that, as packages are routed through the line, the team will know what to do, step by step, to avoid potentially troublesome issues.

9. Don’t overlook final packing and shipping. Imagine spending many days building a product, only to have it be damaged in transit, or even sooner, because not enough attention was paid to protecting it while it was being prepared for shipment to the customer. Not a good feeling. So, when you reach the end of manufacturing cycle, don’t take your eyes off the ball — make sure, as the finished product is being readied to send to the customer, that it’s properly packed to avoid any breakage during that process or once it’s shipped. And check to make sure the customer’s receiving department is notified to expect them — they won’t want to have to pay to replace those parts.

10. Learn from the past. Although we’re continually creating more advanced chips and new materials, the basics of chipmaking and packaging haven’t changed. If you’ve worked on the process side, you understand that future developments are rooted in the work that has gone before — both successes and failures. Keep this in mind as you dig in and learn by doing the hands-on work that keeps our industry moving forward.