How to prevent holes in plating and welding?

Preventing holes in plating and welding involves testing new manufacturing processes and analyzing the results. Plating and welding voids often have identifiable causes, such as the type of solder paste or drill bit used in the manufacturing process. PCB manufacturers can use a number of key strategies to identify and address common causes of these voids.

1.Adjust the reflux temperature curve

One of the ways to prevent welding cavities is to adjust the critical area of the reflux curve. Giving different stages of time can increase or decrease the likelihood of voids forming. Understanding the ideal return curve characteristics is essential for successful cavity prevention.

First, look at the current Settings for the warm-up time. Try increasing the preheating temperature or extending the preheating time of the reflux curve. Solder holes may form due to insufficient heat in the preheating zone, so use these strategies to address the root cause.

Homogeneous heat zones are also common culprits in welded voids. Short soaking times may not allow all components and areas of the board to reach the necessary temperature. Try to allow some extra time for this area of the reflux curve.

2.Use less flux

Too much flux can aggravate and usually lead to welding. Another problem with the joint cavity: flux degassing. If the flux does not have enough time to degass, excess gas will be trapped and a void will be formed.

When too much flux is applied to the PCB, the time required for the flux to be completely degassed is extended. Unless you add additional degassing time, additional flux will result in weld voids.

While adding more degassing time can solve this problem, it is more effective to stick to the amount of flux required. This saves energy and resources and makes the joints cleaner.

3.Use only sharp drill bits

The common cause of plating holes is poor through hole drilling. Dull bits or poor drilling accuracy can increase the likelihood of debris formation during drilling. When these fragments stick to the PCB, they create blank areas that cannot be plated with copper. This compromises conductivity, quality and reliability.

Manufacturers can solve this problem by using only sharp and sharp drill bits. Establish a consistent schedule for sharpening or replacing drill bits, such as quarterly. This regular maintenance will ensure consistent through-hole drilling quality and minimize the possibility of debris.

4.Try different template designs

The template design used in the reflow process can help or hinder the prevention of welded voids. Unfortunately, there is no one-size-fits-all solution to template design choices. Some designs work better with different solder paste, flux, or PCB types. It may take some trial and error to find a choice for a particular board type.

Successfully finding the right template design requires a good testing process. Manufacturers must find a way to measure and analyze the effect of formwork design on voids.

A reliable way to do this is to create a batch of PCBS with a specific template design and then inspect them thoroughly. Several different templates are used to do this. The inspection should reveal which formwork designs have an average number of solder holes.

A key tool in the inspection process is the X-ray machine. X-rays are one of the ways to find welded voids and are especially useful when dealing with small, tightly packed PCBS. Having a convenient X-ray machine will make the inspection process much easier and more efficient.

5.Reduced drilling rate

In addition to the sharpness of the bit, the drilling speed will also have a great impact on the plating quality. If the bit speed is too high, it will reduce accuracy and increase the likelihood of debris formation. High drilling speeds can even increase the risk of PCB breakage, threatening structural integrity.

If holes in the coating are still common after sharpening or changing the bit, try reducing the drilling rate. Slower speeds allow more time to form, clean through holes.

Keep in mind that traditional manufacturing methods are not an option today. If efficiency is a consideration in driving high drilling rates, 3D printing may be a good choice. 3D printed PCBS are manufactured more efficiently than traditional methods, but with the same or higher accuracy. Selecting a 3D printed PCB may not require drilling through holes at all.

6.Stick to high quality solder paste

It is natural to look for ways to save money in the PCB manufacturing process. Unfortunately, buying cheap or low-quality solder paste can increase the likelihood of forming weld voids.

The chemical properties of different solder paste varieties affect their performance and the way they interact with the PCB during the reflux process. For example, using a solder paste that does not contain lead may shrink during cooling.

Choosing a high quality solder paste requires you to understand the needs of the PCB and template used. Thicker solder paste will be difficult to penetrate a template with a smaller aperture.

It may be useful to test different solder pastes at the same time as testing different templates. Emphasis is placed on using the five-ball rule to adjust the template aperture size so that the solder paste matches the template. The rule states that manufacturers shall use formwork with apertures required to fit five solder paste balls. This concept simplifies the process of creating different paste template configurations for testing.

7.Reduce solder paste oxidation

Oxidation of solder paste often occurs when there is too much air or moisture in the manufacturing environment. Oxidation itself increases the likelihood of voids forming, and it also suggests that excess air or moisture further increases the risk of voids. Resolving and reducing oxidation helps prevent voids from forming and improves PCB quality.

First check the type of solder paste used. Water-soluble solder paste is particularly prone to oxidation. In addition, insufficient flux increases the risk of oxidation. Of course, too much flux is also a problem, so manufacturers must find a balance. However, if oxidation occurs, increasing the amount of flux can usually solve the problem.

PCB manufacturers can take many steps to prevent plating and welding holes on electronic products. Voids affect reliability, performance and quality. Fortunately, minimizing the likelihood of voids forming is as simple as changing the solder paste or using a new stencil design.

Using the test-check-analyze method, any manufacturer can find and address the root cause of voids in reflux and plating processes.