PCB Technical - Factors to be considered in PCBA production process

1. Product functions ofPCBA

For example, it covers the basic requirements, product upgrade functions, additional products can perform functions, and has components that are easy to make and manage.

2.PCBAinvestment return

At present, there are many manufacturers engaged in PCBA design and production, and different manufacturers provide different product quality, cost performance and cost. As a PCBA designer, we must strive to improve product quality, reduce product cost, and provide enterprises with low investment and high return. Therefore, in the process of PCBA design, we should consider all aspects, so as to ensure the final cost and return on investment.

3.PCBApartners

PCBA design can't be completed by one person, it must be completed by teamwork. Therefore, if you want to design a good circuit board, you must have strong team support. ipcb company has stable and mature experience in PCBA production.

Introduction and precautions of double-sided soldering process (SMT) for PCB

Currently, the main technology of circuit board assembly in SMT industry should be "Reflow". Of course, there are other methods of circuit board welding. This kind of circuit board reflow can be distinguished between single-panel and double-panel. Nowadays, few people use single-side reflow, because double-side reflow can save space of circuit board. That is to say, production can be made smaller, so most of the boards seen on the market belong to double-sided reflow process.

(Beyond the question, if there are no space constraints, in fact, the single panel process can save the SMT process. If you compare the material cost with the SMT's work cost, it may be that the single panel will save the cost.)

Because the double-sided reflow process requires two times of reflow, there will be some process limitations. The common problem is that when the board goes to the second reflow furnace, the parts on the top of the surface will fall due to gravity. Especially when the board flows to the high temperature of the reflow zone of the furnace, this paper will explain the points for attention in the placement of the parts in the double-sided reflow process:

(To add another subtitle, why don't most of the small parts that were already tin-coated on the second side of the solder melt back and fall off? Why only the heavier parts fall off?)

Which SMD parts should be placed on the surface of the reflow furnace?

Generally speaking, smaller parts are recommended to be placed in the side-to-side reflow furnace, because PCB will have less distortion and more accurate paste printing, so smaller parts are better placed.

Secondly, the smaller parts are not at risk of dropping off in the second pass of the reflow furnace. Because the parts on the second side will be placed directly downwards on the bottom of the printed circuit board, they will not fall off the board due to excessive weight when the board enters the high temperature of the welded area.

Third, the parts on the panel must be repaired twice, so the temperature resistance must be able to withstand the temperature of two repairs. Normal resistance capacitance is usually required to be repaired at least three times. This is to meet the requirement that some boards may need to be repaired due to maintenance.

Which SMD parts should be placed on the second side of the reflow furnace? This should be the focus.

Large or heavy components should be placed on the second side of the furnace to avoid the risk of parts falling back into the furnace.

LGA, BGA parts should be placed on the second side of the furnace as far as possible to avoid unnecessary risk of remelting tin in the second pass, and to reduce the chance of empty/false soldering. If there are slim legs and small BGA parts, it is not excluded that it is recommended to place them on the surface of the back weld furnace.

BGA placing on the side or on the second side of the stove has been controversial. Although placing the second side can avoid the risk of re-melting tin, PCB usually deforms more heavily when the second side passes through the reflow stove, which can affect the quality of tin eating, so working bears will say that BGA with slim feet can be considered on the side. However, on the other hand, if the PCB is badly deformed, it must be a big problem to place the second side patch on the delicate parts, because the paste printing position and the amount of paste will become inaccurate, so the focus should be on how to avoid the PCB deformations, rather than consider placing the BGA on the side because of the deformations, shouldn't it?

Parts that cannot withstand too many high temperatures should be placed on the second side of the reflow furnace. This is to avoid damage to parts due to too many high temperatures.

PIH/PIP parts should also be placed on the second side of the furnace. Unless their solder feet are not longer than the thickness of the plate, their feet extending out of the PCB surface will interfere with the plate on the second side, which will prevent the plate printed on the second side from sticking flat to the PCB, causing anomalous solder printing problems.

Some components may have solder work inside them, such as wire connectors with LED lights. It is important to be aware that the parts can withstand temperatures more than twice in a reflow furnace, and if not, they must be placed on the second side.

Just placing the part on the second side of the patch in the back-weld furnace means that the circuit board has passed the baptism of the high temperature of the back-weld furnace. At this time, there is more or less some warping and distortion of the circuit board. That is to say, the amount and position of the solder paste printing become more difficult to control, so it is easy to cause problems such as empty welding or short circuit, so placing the part on the second side of the back-weld furnace, It is recommended to avoid placing 0201 and fine pitch parts as far as possible, and the BGA should also try to select tin balls with larger diameters.

Referring to the pictures on the front and back sides of the SD card board in the article, you should be able to make a clear judgment and point out that the side will be arranged in the surface-beating parts to be repaired in the furnace, and the side will be put in the second side of the patch to be overheated.

In addition, there are many processes for assembling electronic components to the circuit board in mass production. However, each process has been decided at the beginning of the circuit board design, because the placement of the components on the circuit board will directly affect the assembly welding order and quality, while wiring will indirectly affect it.

Currently, the welding process of printed circuit board can be roughly divided into full-plate welding and local welding. Full-plate welding can also be roughly divided into Reflow Soldering and Wave Soldering, while local welding of printed circuit board can be Carrier Wave Soldering, Selective Soldering and Laser Soldering. Wait.