Wave soldering process for DIP assembly

Wave soldering is a mechanism introduced by Albert Hanson (German inventor) for the soldering of hundreds of components on a Printed Circuit Board in a minimum amount of time. In this process, the printed circuit board (PCB) passes over a pan of molten lava through a conveyer belt. A pump fixed under a conveyer belt directs the solder (molten) on the circuit board in such a way that it gives a visual of a wave hitting on the surface of the circuit board. It is to be said that PCBA soldering came into existence right after the discovery of tin, which is still a significant element of soldering paste.

The concept of a flat with many layers including an insulating layer and a foil conductor was introduced by German inventor Albert Hanson. Moreover, he gave an idea of drilling holes in the board, which is almost the same PCB DIP assembly technique used to mount through-hole components today. After this, companies started producing components in through-hole DIP packages. So, it was simpler to apply solder paste to the entire board at once rather than soldering each individual electronic component using a soldering iron. As a result, wave soldering was invented, in which the complete board passed over a solder.

Nowadays, wave soldering machines are performing the art of soldering the components automatically. Next, FS Technology will explain in detail how wave soldering works.

How does Wave Soldering work?

The wave soldering process in the entire DIP assembly process includes 5 steps: Solder Melting, Components cleaning, PCB Placement, Soldering, Cleaning. Next we will explain each step.

Step 1: Solder Melting

The wave soldering machine has a container filled with solder, which is heated at a temperature of 180 to 450 °C depending on the type of solder and the model of the soldering machine. This is the most key step of all because the solder is supposed to be melted in its purest form. Temperature precision is very vital for this role. It will ultimately bring consistency and smoothness to the process and gain better results.

Step 2: Components cleaning

In this step, the components to be placed on the PCBA go through a process of thorough cleaning. You must check to see if there are any oxide layers during cleaning. If yes, then you must clean them first. Besides, it would be beneficial to prevent them from developing oxide layers. The chemical used for the cleaning of components is known as flux. PCB flux is actually a mixture of base material and an activator that is used for the better wetting of the solder by removing oxides from the metal.

Step 3: PCBA Board Placement

In this step, we place the components on the circuit board and get the PCBA ready to be placed in the wave soldering machine. Then we place the assembled boards inside a machine and make sure that the board is precisely attached to the conveyer belt at a 0° angle. For this, metal clasps are available in the wave soldering machine to hold the circuit board and don’t allow it to move a single bit.

Step 4: Soldering

This is the main step of the process, where we achieve our goal of soldering the PCB components on the circuit board. So here the board is moving with the conveyer belt and finally the board approaches above the solder pan. Here, we make sure the speed of the conveyer belt is low so that the excessive solder should drain back into the solder bath. We make sure that the solder settles within the joints completely.

Step 5: Cleaning

We can call it a cosmetic step of the process where we clean the product. In this step, we wash the circuit board with multiple solvents and deionized water to remove the remaining flux residues on it. The most common solvent used for the removal of flux is isopropyl alcohol because it’s cheap and non-toxic as compared to the other solvents available for the same job.

How does the wave soldering machine work?

A wave soldering machine is a necessary device for achieving through-hole PCB assembly. Due to the different equipment used, the manufacturing capabilities of PCBA manufacturers are very different, and the audit of their equipment is also necessary when you are screening service providers. For example, when your project requires SMT assembly, you must pay attention to how many temperature zones the reflow soldering equipment used by the service provider has. If you need DIP assembly services, focus on observing whether they can achieve fully automatic assembly and whether the wave soldering machine can achieve mass production.

Flux Sprayer:

There are only two actions a spray fluxing system performs. First, put wave soldering flux where it should be, which is into the plated holes of your circuit board. And second, put the right amount of flux there. Every component of a quality fluxing system ought to be focused on achieving these two objectives. Regardless of the width, thickness, or hole diameter of your circuit board, a properly designed fluxing system will get flux into the plated holes of your board.

Preheating pad:

Although wave soldering can be done without preheating, the soldering process will take comparatively more time. In The Handbook of Machine Soldering SMT and THT, Woodgate mentions, “During some experimental work with preheating, a board was soldered at 12 ft. per minute with the normal preheat applied. Without preheating it could not be soldered faster than 2.5 ft. per minute.” Here FS Technology provides four reasons why wave soldering must be preheated:

The solvent component of the flux is evaporated by heat with the help of a preheater to increase the flux activity.
Prevent the formation of solder balls by drying the flux solvent, otherwise it will spit out when encountering solder waves.
Minimize the thermal impact of wave soldering on the PCB, thus controlling the warpage and other failures brought about by the sudden rise in temperature.
The last and most important reason is to heat the components, boards and the rest of the connector so that DIP soldering can proceed faster and more smoothly.

Pump:

The linear motor pump for a wave soldering device consists of various pumping channels that are oriented essentially parallel to one another and apart from one another. Preferably, it has a stator with many segments. One pumping channel is allotted to each station. This results in a homogeneous pumping performance, or homogeneous pumping pressure distribution over a virtually arbitrary breadth, and a homogeneous solder wave. A chaotic whirling of the solder is virtually impossible, thanks to the positioning of the pumping channels and the invention’s stator design.

Analysis of the pros and cons of wave soldering

Advantages of Wave Soldering

Ideal for lead-free process requirements that demand high productivity.
There is no need to mask off board areas that don’t need to be soldered.
Selective soldering equipment is typically less expensive to run.
It has adjustable parameters that can be more precisely regulated.
The equipment’s noise level is under 60 db.
Stepper motor-driven spraying, adjustable tin spraying mouth design, automatic positioning spraying and tin spraying, 25% less power, and auxiliary material consumption year over year.
Closed-loop control of the transport system, precise preheating, and welding time control.
Very little tin dross oxidation occurs near the crest of a flat-flow wave, and a humped laminar flow wave tends to produce flawless solder joints.

Drawbacks of Wave Soldering:

The use of reflow soldering has increased due to the introduction of surface mount devices (SMDs) and multiple-layer boards. The best soldering technique is reflow if your PCBA just contains SMD components. However, wave soldering will probably be used if your PCB design also uses through-hole components or does so solely. The type of wave soldering procedure employed depends on the number of components, their spacing on the board, and the length of the PCB run. Your design determines each of these.