caLogo

Defect of the Month

Bob Willis

When through-hole connectors move during soldering, damage to the nozzle ensues.

This month we we look at through-hole connectors and component pin float. All connector pins should be held in place by the body molding and not move during soldering. The connector should not be used outside of its specification. Suppliers typically define the temperature and time the pins and body of the part are exposed to a specific peak temperature. It is the designer’s job to ensure the correct parts are defined for the process. It is the purchasing department’s job to ensure the correct parts are ordered.

In the images shown, the pins in the connector have floated down. This happens easily during soldering or rework. In an automated process, if the pins drop down 1 to 2mm below the board in selective or wave soldering, they can cause damage. Pins can contact the solder nozzle or wave former, which will jam the machine. Using low-temperature solder with a lower specification connector will work fine, but consider the rework temperatures if parts must be removed.

 

To continue reading, please log in or register using the link in the upper right corner of the page.

Read more ...

Bob Willis

Moisture is only one of the potential culprits.

PCB delamination can be subtle or obvious. It is caused by expansion of moisture in the PCB laminate, but that may not be the root cause. Eliminating moisture often prevents the energy buildup that forces apart different layers, but this is not the complete story. Poor bonding during manufacturing of the multilayer board or some form of contamination may result in poor adhesion on innerlayers, permitting moisture to accumulate on these surfaces.

FIGURE 1 shows solder mask cracking around a through via. The PCB expanded during reflow, then contracted during cooling. This resulted in lifting and cracking of the solder mask, plus an intermittent electrical connection. FIGURE 2 shows the innerlayer surface of the board after separation. The through vias are separated and there is no visible adhesion on this layer.

 

To continue reading, please log in or register using the link in the upper right corner of the page.

Read more ...

Bob Willis

Solder joint corrosion causes.

This month we illustrate dendrites and corrosion on board assemblies. The example in FIGURE 1 is straightforward. Saltwater was found on the surface of the metal board. It caused intermittent operation of the LED before failure at 25 meters. Yes, you guessed it: My underwater light leaked due to a rubber gasket failure. The rubber had been out in the sun too long and hardened, then cracked. The image shows chemical reaction with dendrite formation on the surface of the joints and some green verdigris.

 

 

 

To continue reading, please log in or register using the link in the upper right corner of the page.

Read more ...

Bob Willis

Be sure to optimize the preheat to improve wetting.

This month we we illustrate high-temperature soldering of through-hole connectors. In this case both the PCB nickel/gold surface and the tin surface of the pin were perfectly solderable. The time to preheat the board and connector before soldering was not optimized for robotic soldering, however. To obtain the correct process setting, balance all settings, but to increase throughput in an inline process using a robot, many applications require preheating. Robots are flexible, but an operator can see and judge the time required.

 

 

 

Read more ...

Bob Willis

Soldering in nitrogen or vapor phase environments can increase the likelihood.

Subtle component lifting can be an issue to find during inspection. Most modern AOI systems should be able to detect drawbridging on small passive and active parts. Old systems may struggle with defects like the two shown in FIGURE 1.

 

 

 

 

Read more ...

Bob Willis

Get the right stencil for the job.

This month we illustrate an example of what appears at first glance to be poor lead solderability. When examined, however, it is a combination of component and pad design.

FIGURE 1 shows the lead to be floating in the solder joint, suggesting poor wetting. When we examine the component lead and plastic body, however, the lead is not parallel, so it always sits off the pad surface, even if perfectly soldered. The lead sits in a cavity in the component body to maintain its position. But with the size of the pad used in the design and a full solder paste print, the component body will always lift.

 

To continue reading, please log in or register using the link in the upper right corner of the page.

Read more ...

Page 3 of 14

Don't have an account yet? Register Now!

Sign in to your account