In the process of multi-variety and small-batch military production of circuit boards; many products also require lead-tin plates. Especially for high-precision printed PCB multilayer boards with many varieties and very few quantities, if the hot air leveling process is used, the manufacturing cost will obviously be increased, the processing cycle will be long, and the construction will be very troublesome. For this reason, more lead-tin plates are usually used in PCB manufacturing; however, there are many quality problems caused by circuit board processing. One of the bigger quality problems is the quality problem of delamination and blistering after infrared thermal melting of the lead-tin coating of multilayer printed circuit boards.
In the graphic electroplating process method, the tin-lead alloy layer is generally used for printed pcb multilayer boards; it is not only used as a graphic metal resist layer, but more importantly, it provides a protective layer and a soldering layer for the lead-tin plate. Because of the pattern electroplating-etching process, after the circuit pattern is etched, the copper layer on both sides of the wire is still easy to contact with the air to form an oxide layer or be corroded by an acid-base medium.
In addition, because the circuit pattern is prone to side erosion during the etching process, the tin-lead alloy plated part is in the air, resulting in a suspension layer. And it is easy to fall off, causing a short circuit due to bridging between the wires. The exposed copper surface can be extremely well protected by using the infrared hot-melt process. At the same time, the tin-lead alloy coating on the surface and in the hole can be crystallized after infrared heat melting, so that the metal surface is shiny. It not only improves the solderability of the connection point but also ensures the reliability of the connection between the components and the inner and outer layers of the circuit. However, when it is used for infrared thermal melting of multilayer printed circuit boards, due to the high temperature, delamination and blistering between layers of PCB multilayer circuit boards is very serious, resulting in extremely high yield of multilayer printed circuit boards. Low. What causes the quality problem of delamination and blistering of multilayer printed circuit boards?
Causes of PCB multilayer circuit board:
(1) Insufficient glue flow;
(2) The inner circuit board or prepreg is polluted;
(3) Improper suppression leads to the entry of air, water vapor and pollutants;
(4) Poor blackening treatment of the inner layer circuit or the surface is polluted during blackening;
(5) Excessive glue flow - almost all the glue contained in the prepreg is extruded out of the board;
(6) During the pressing process, due to insufficient heat, the cycle is too short, the quality of the prepreg is poor, and the function of the press is not correct, resulting in problems with the degree of curing;
(7) Under the requirement of no function, the inner layer board should minimize the appearance of large copper surface (because the bonding force of resin to copper surface is much lower than the bonding force of resin to resin);
(8) When vacuum pressing is used, the pressure used is insufficient, which will damage the glue flow and adhesion (the residual stress of the multi-layer board pressed by the low pressure is also less).
Solutions for PCB multilayer circuit boards:
(1) The inner layer circuit board needs to be baked and kept dry before lamination and pressing.
Strictly control the process procedures before and after pressing to ensure that the process environment and process parameters meet the technical requirements.
(2) Check the Tg of the pressed multilayer board, or check the temperature record of the pressing process.
The pressed semi-finished product is then baked at 140° C. for 2-6 hours to continue curing.
(3) Strictly control the process parameters of the oxidation tank and cleaning tank of the blackening production line and strengthen the inspection of the surface quality of the board.
Try double-sided treated copper foil (DTFoil).
(4) The cleaning management of the operation area and storage area needs to be strengthened. Reduce the frequency of manual handling and continuous board removal.
All kinds of bulk materials in the lamination operation need to be covered to prevent pollution.
When the surface treatment of the tool pin must be lubricated and out of pins, it should be separated from the stacking operation area and cannot be carried out in the stacking operation area.
(5) Appropriately increase the pressure intensity of pressing.
Appropriately slow down the heating rate to increase the flow time, or add more kraft paper to ease the heating curve.
Replace prepregs with higher flow rates or longer gel times.
Check whether the surface of the steel plate is smooth and free of defects.
Check whether the length of the positioning pin is too long, causing the heating plate not to stick tightly and resulting in insufficient heat transfer.
Check whether the vacuum system of the vacuum multi-layer press is in good condition.
(6) Properly adjust or reduce the pressure used.
The inner board before pressing needs to be baked and dehumidified, because the moisture will increase and accelerate the flow of glue.
Switch to a prepreg with lower flow rate or shorter gel time.
(7) Try to etch away the useless copper surface.
(8) Appropriately and gradually increase the pressure strength used for vacuum pressing until five times of float soldering tests (each at 288°C, 10 seconds) are passed.
