Assembling a Printed Circuit Board

When the design and fabrication of a printed circuit board is done, it is time to assemble it. Assembling printed circuit boards require another set of processes to follow.The first three processes are drilling, plating and coating, solder resist application. These are followed by legend printing, board testing, and protection and packaging.
 

Drilling holes is the first process in assembling.

PCBHoles are drilled using drill bits which are very small. They should be made of solid coated tungsten carbide. It is recommended that they are coated because many board materials are abrasive. To ensure cost-effectiveness, drilling should be done at high RPM and high feed. Additionally, drill feeds have to be very sharp.Drilling is usually performed using automated machines. The placement of these drilling machines is controlled by computer-generated drill files. The drill file automatically locates the hole and knows the size of each drilled hole.
 
All the holes can be made conductive through electroplating and inserting metal eyelets.They are made conductive in order to electrically and thermally connect board layers. Another option is to connect only some of the copper layers rather than passing through the entire board. This can be done through controlled-depth drilling. For boards with two or more layers, they are made conductive and electroplated with copper through plated-through holes.
 

The next process is plating and coating.

A printed circuit board is usually plated with gold over nickel, tin and solder. This is done to resist etching away the underlying copper, which is not needed.After etching, the PCBs are rinsed with water. Then, solder mask is applied. Other exposed copper is coated to avoid corrosion.
 
After plating and coating, the next process is solder resist application. The surface that should not be soldered will be covered with solder mask. Legend printing is when symbols, letters and numbers are printed on either one or both sides of the printed circuit board. It has the designators, test points, switch settings, and other helpful indications for assembling, testing and servicing the board.The three methods used to print the board are silk screen printing with epoxy ink, liquid photo imaging, which is a more accurate method, and ink jet printing.
 

The next phase is the bare-board test.

They are tested for shorts – connections that should not be together. They are also tested for opens, which are missing connections, making them the exact opposite of shorts.
 
The next phase in the assembly process is when the bare boards are populated with electronic components. These are done through two known methods: through-hole technology or surface-mount technology. In both methods, component leads are mechanically fixed and electrically connected to the board through soldering. There are many soldering methods used to fasten components to a printed circuit board.
 
pcb-green

It is important to test a populated board.

Testing is also done in a variety of ways. That includes visual inspection and even an automated optical inspection. There is also power-off testing while the power is turned off. On the other hand, there is an in-circuit test as well as a functional test when the power is on. The question is what happens when boards fail the test?The boards are then soldered again and failed components are replaced. This is referred to as reworking.
 
The last part of the process is protection and packaging. Printed circuit boards that will be placed in extreme environments will have conformal coating. Conformal coating is applied by dipping or spraying after soldering. This coating prevents corrosion and leakage. Conformal coats are dips of silicone rubber or polyurethane solutions. Many PCBs are placed in antistatic bags during transport.

Of Custom Coins and Bar Challenges

We at www.ChallengeCoins4Less.com deal with numerous requests for custom coins and do so on a daily basis. The thing that always surprises us is that most of the people who commission coins are unaware of the lengthy history of the challenge coin. We ourselves have an idea of how the first challenge coin came to be, but there seem to be inaccuracies in the so-called official stories that we know or have heard about.

Custom CoinsIt is safe to say that no one is certain as to how these custom coins came to be, but there is a story, which dates back to the First World War that sounds as the most legitimate record there is. As the story goes, there was a wealthy officer in the army and he was known for handing out engraved bronze medallions to his men. These tokens were marked with their flying squadron’s insignia.

After some time, one of his flying aces was shot down by the Germans. They took everything from him except the pouch which contained the coin. Luckily, he was able to escape making his way to France where he was mistaken for a German spy and scheduled to be executed had he not presented his medallion which confirmed his identity as an American ally.

Based on historical records, one of the earliest coins of this kind was actually minted by a Colonel from the 17thInfantry Regiment, a man by the name of Buffalo Bill Quinn. The Colonel had the tokens made for his men during the Korean War. On one side is the image of a buffalo. On the other side was the Regiment’s insignia.

Instead of carrying the tokens in a pouch, he had a hole drilled on top of each coin allowing his men to wear it on their necks pretty much like a traditional dog tag. The kind of custom coins created at www.ChallengeCoins4Less.com may come with or without this feature. Basically, it depends on what our customer wants.

Aside from where these challenge coins originated from, we also share with our clients the tradition of making a challenge using these tokens. Once used as organizational medallions, these coins started to be used for challenge pitches after the Second World War. Surprisingly enough, the challenge component of these coins began in Germany.

Back in the day, there was a local German tradition referred to as pfennig checks. Now the pfennig was a coin that bore the lowest currency denomination. When a check is called between friends and colleagues and you did not have one in your person, you will be obligated to buy beers for everyone.

From the pfennig, the tradition soon changed to using challenge coins instead.

Especially within military ranks or organizations, members would challenge each other with the symbolic slamming of a challenge coin on a table. Someone challenged that did not have theirs at that time will be obligated to buy a round of drinks for the challenger and everyone on the team carrying their custom coins but if the one challenged has a coin to show, it will be the challenger buying the drinks for everyone with a coin.

We often tell people that these coins are not only group medallions, tokens, or something you use to make a bar challenge. It is something, which involves an internal understanding and exchange of respect between people especially considering that the concept originated from the military.

Another interesting tidbit about challenge coins is that there is a secret handshake, which is done whenever a coin is exchanged between military men. To the naked eye, it may seem like an ordinary handshake, but for those within the ranks, it means a completely different thing. That simple handshake means something more and says tons without the utterance of any word.

This secret handshake is a tradition upheld by military men. It is said that this exchange originated in the Second Boer War of the 20th century. It was a war between the British and South Africans. The British employed mercenaries to join their troops and because of their status, were not eligible to receive medals of valor for their service. This is why commanding officers rewarded them, in secret, with challenge coins instead.

The tokens were obtained from unjustly awarded soldiers. Officers who were non-commissioned will sneak into the formers’ tents and cut the medallion from their ribbons. These were then passed on to the mercenaries via handshake, indirectly thanking them for their service and sacrifice.

These days, military forces still use these custom coins but other organizations are following suit from non-government units to special clubs and groups. Probably the coolest, and most collectible, coins we have seen are those carried by White House Military Aides. These are referred to as the “Atomic Football” and they are indeed in the shape of a football.