Because BGA (Ball Grid Array) solder balls are hidden under the body, it’s quite difficult to inspect their performance. Up to now, Automated X-ray Inspection is applied to help exposing the defects of BGA solder balls including void, displacement, bridging, cold solder etc. Once defects are found out, rework has to be implemented. However, rework always costs a lot, which is absolutely NOT called for by OEMs. Therefore, it is first and foremost to guarantee the quality of BGA solder balls by effectively stopping solder defects from being generated. So, this article will discuss the key elements to be captured in the process of SMT assembly.
It’s necessary to indicate that all the tips are summarized based on manufacturing experience workshop. has been serving globe electronics for 10 years. Up to now, we’ve served more than 1000 customers from over 20countries and regions around the world with HIGH-RELIABILITY and LOW-COST bare PCBs and assembled PCBs that have been widely applied in numerous fields covering medical care, industrial control, transportation, military, aerospace, IoT etc.
Before Soldering
PCB Board Preparation
First, proper surface finish should be picked up to be compatible with project or product requirement. There are a couple of surface finishes available and surface finish introductions and comparison should be clear in your mind. Some products call for ROHS requirement and lead-free surface finish, lead-free HASL, lead-free ENIG or lead-free OSP can be applied.
Second, PCBs should be properly stored and applied. PCBs should be packed in vacuum and container should include moisture barrier bag and moisture sensitive indicator card. The indicator card is capable of conveniently and economically inspecting whether humidity is in the control range. The color on card can be seen to tell about the humidity within the bag and the effect of desiccant. Once the humidity inside the bag exceeds or equals indicator value and the corresponding circle will become pink.
Third, PCBs should be baked and/or cleaned. Baking can be implemented on PCBs to stop moisture from leading to soldering defects. Baking can be carried out under the temperature of 110±10℃ for two hours. Also, PCB surface may be covered by dust in the process of PCB moving and storage. Therefore, it’s so important to thoroughly clean PCBs prior to assembly. ultrasonic cleaner is used on assembled PCBs to guarantee them to be totally clean. As a result, board reliability can be greatly ensured.
BGA soldering, Reflow Technology soldering
Typically, the assembly package of BGA is the same as the SMT assembly. First, solder paste gets printed on a pad array of a PCB by applying stencil or flux onto the pad. Secondly, you introduce the pick-and-place equipment to align BGA components on the PCB. After that, subject the BGA components through a reflow soldering oven. Reflow technology soldering is a complicated process that involves a couple of phases, as briefly highlighted below:
- Preheating phase –this phase is usually composed of 2 to 4 zones of heating. Here, the temperatures can go as high as 150℃ in under 2 minutes. For this reason, there are no instances of solder splashing or an overheated base.
- Soaking phase – here, the target is to achieve hot melting, something that makes good soldering joints.
- Soldering phase –this phase needs to witness the temperature of solder joints rising to that of the soldering temperature. Here, it’s best to set high temperatures so that the joints come out as desired.
- Cooling phase –this is the last step of reflow technology soldering. It contains two modes of cooling: natural cooling and air cooling. It’s ideal for the cooling rate to be between 1 ℃ and 3℃.
Control the Solder of BGA Soldering
The fifth step is to ensure that you control the solder during the BGA soldering. On most occasions, when soldering, the temperature surpasses the melting point, with the solder getting melted to become liquid.
But to ensure that everything comes out as desired, you must control the solder of BGA soldering. You achieve this by maintaining temperature levels of about 183 degrees for 60 to 90 seconds. Either too long time or too short time frames may cause quality issues when undertaking BGA soldering. Sometimes, you may have to check your soldering knob. A majority of them have a knob when turned, reduces the heat of the iron. It thereby controls the solder and lets you have the desired results.
Best BGA solder Joint Standard
There are specific BGA solder joint standards that you must adhere to if you want to undertake BGA soldering on PCBs during SMT assembly. For instance, BGA soldering joints that have cavities in them lead to many failures. They are also likely to have other costly technical issues in the long run.
For instance, according to IPC BGA soldering standards, if it is challenging to avoid cavities on the pad, such holes shouldn’t be 10% larger than the solder ball area. In other words, the tunnels on the pads must not be larger than 30% compared to the solder ball’s diameter. To ensure good results, you may have to stick to acceptable industry standards regarding BGA solder joints.