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How To Make Heavy Copper PCB?

1.With the rapid development of communication technology in automotive electronics and power supply, 10OZ and above ultra thick copper circuit board has gradually become a kind of special PCB board has broad market prospect, by the circuit board manufacturers more and more attention, at the same time with the printed circuit board is used more and more widely in the field of electronic equipment, are increasingly high demands on the PCB printed circuit board, we will not only provide the necessary electrical connection and mechanical support for electronic components, but also gradually endowed with additional functions, and can be integrated, power provided extra thick copper printed circuit board for high current and high reliability products PCB industry has gradually become a hot research. The products used for military products.

At present in the industry to do more of the PCB copper foil thickness is usually between 2OZ~4OZ, and for the finished copper 10OZ thick and ultra thick copper PCB production reports over almost no, this paper mainly focuses on the key process of 10OZ super thick copper PCB production technology and production control in the process of the follow-up, finally found make an ideal process route and conditions of ultra thick copper PCB.

2 Experiment

2.1 Experimental materials and equipment

(1) FR-4 substrate, in which the plate thickness is 1.6mm, the copper thickness is 4OZ

(2) The conventional equipment for making PCB in our company

2.2 Process design

This experiment is a double sided printed circuit board made of copper with a thickness of 10OZ. The specific experimental process is:

Cutting —> Drilling positioning hole—>Pattern transfer —> Pattern electroplating—>Fading film, Etching—> Solder mask printing —> Solidification after solder mask printing —>Copper plating —> Pattern transfer pattern —>Plating —>Etching—>Fade film and Ethching—>Solder mask printing—>Solidification after solder mask—> Drilling —>Copper, plating —>Pattern transfer—>Pattern plating—>Etching—>Fade film and etching—>Solder mask printing—>Solidification after solder mask—> Test—>Outline milling—>Final product inspection

For the “Pattern transfer —> Pattern electroplating” process, this experiment designed three kinds of production solution:

Solution 1: wet film method, its main idea is: using the wet film making good filling of the deck will pave the way and pattern transfer, then electroplating two cycles, thickened about 2OZ thickness, that is based on the thickness of the 2OZ stack, the specific process as shown in Figure.2

heavy copper process

Solution 2: a dry film method, its main thought is: after making paste dry film for LDI production line, and then electroplating a cycle, thickened about 1OZ thick, with the thickness of the 1OZ stack, the specific process is shown in figure 3.

heavy copper process-

Solution 3: two times dry film method, its main thought is: after the first production line of LDI paste dry film making, and plating a cycle (about 1OZ thickness), the basic level of dry film and then paste again dry film line, LDI line, and then a cycle of plating (about 1OZ thickness), with the thickness of the 2OZ stack, specific process as shown in Figure 4.

heavy copper process-3

3.Results and discussion

3.1 Optimization of process

The solution 1 was typical of the mushroom lines, and the two lines appear obvious dislocation, dislocation of two main reasons is used to line the film pattern transfer with wet film, and the film on artificial alignment is guaranteed: the line appears mushroom is mainly due to wet the thin film thickness of artificial printing (about 1/3OZ), the late electroplating copper (the thickness of about 2OZ) caused by protruding lines.

Two dry membrane stacks up to two times by solution 3 design does not appear mushroom lines, compared to the wet film made by the method of lines have been greatly improved, the reason lies in the analysis of dry film production line method with the LDI (laser direct imaging) in line alignment, alignment can be guaranteed degree, and because the dry film thickness is about 1OZ, and a circulation of only thick plating thickness of about 1OZ, and the time of plating basically does not appear mushroom line.

In solution 2,once posted film made in the dry line alignment degree compared to the three schemes two dry line film made by the method of sticking to some poor, the main reason is that with a dry film lamination method to make the circuit when the solder alignment is 7 times, and two times of dry film making method when the number of resistance welding line alignment is only 4, obviously artificial resistance welding para number line dislocation is more obvious, in addition to the solder alignment number, production cycle is long, so the quality and delivery time from the two aspects, solution 3 is more advisable than solution 2.

Through the above analysis, it can be seen that solution 3 (two times foil method) is an ideal process flow for making extra thick copper foil circuit board.

3.2 Control of special process

3.2.1 Graphic electroplating

The copper thickness of the circuit is thickened by pattern plating, so that the line is in accordance with the dry film, so as to facilitate the next sticking of the dry film. The current pattern plating than the actual calculated value is smaller, generally small 2~3A is appropriate, and timely to try hand surface roughness, avoid copper electroplating and showed protruding lines like mushrooms, also at the time of plating in the plate around the clamp at the same time reversed flow the printed circuit board in the direction to improve the uniformity of copper plating.

3.2.2 Solder Resist

In the production process of solution 3, the pre-printed solder mask is mainly used to pave the flat surface before the last printing resist welding, so as to make the later dry film tight.

heave copper process-4

Specific operations should be controlled in the following aspects:

a.Uses two printing plate oil way, first use 43T screen, still time to do a proper extension, in order to eliminate the line between bubbles, 77T use pre baked screen second times normal static ink, baking plate. The board should be placed horizontally in case of standing and drying to prevent vertical flow.

b. Exposure, the exposure energy energy than ordinary plate is slightly lower, t-stops control in about 10, to prevent light scattering and developing without a net, and then causes the ink into the graphics have obvious “ladder” line.

3.2.3 Solder resist curing

Resistance welding after curing, curing and to segment at the highest temperature (150 DEG C) to add baked 30min, the reason is that the solder after the board next to the copper deposition, if the ink curing is not sufficient, so the heat resistance, chemical resistance will be very poor, strong alkaline substances will sink with ink culink in not completely cured the acidic resin reaction of neutralization reaction, causing the ink off.

3.2.4 sinking copper and plate electricity

Copper prior to mechanical pretreatment, in order to improve the surface roughness, increase the surface area, and increase the adhesion between the copper layer and the surface of the sink. In the process of copper deposition in the board on the swelling tank and glue residue in the groove of the time can not be too long, generally 5~7min is the best, the board has enough activity, if longer, so it is possible to erosion ink not resist alkali caused by solder layer off.

Before the board power, the board should be baked at 100 degrees 1h to remove the moisture between the copper sink and the solder layer, and then improve the bonding force between the two, and prevent the copper layer blister after the board electricity and cause the fall off. When the plate is charged, a cycle is plated with the current density of 1.2ASD, and the copper thickness of the surface can reach about 1/3OZ.

3.2.5 key process etching

General copper clad plate, surface copper thickness is HOZ~2OZ, but for the thick copper printed circuit board, the surface copper thickness reached more than 3OZ, the etching inevitably adopts multiple etching, etching the number of lateral erosion is more serious, affecting the accuracy of line is also bigger.

For this experiment, the later layers on line in copper plate, electric (about 1/3OZ thick copper) on the basis of production, that is to say in pattern etching, etching the base copper thickness need only about 1/3OZ, now basically does not exist side etching. But it is important to consider is to end the 4OZ copper material side erosion graphic etching, we need proper compensation for the line, with its lateral erosion make up, make the lines precision to meet the design requirements. Table 1 shows the relationship between the thickness of copper foil and the amount of single side etching.

heavy copper PCB process-5

4. Conclusion

By sticking two times dry film layer by layer stacking method is an ideal process route for making super thick copper PCB plate. It not only can ensure alignment of the line, but also can effectively avoid mushroom like lines appear

Through the B. line to thicken pattern plating copper thickness, its current value is slightly smaller than the actual calculated by 2~3A; solder resist ink paved surface, the exposure energy is slightly lower than ordinary board, solder after curing, curing and to segment at the highest temperature (150 degrees Celsius) to add roast 30min: copper before mechanical pretreatment, and to shorten the board in the swelling and glue residue in the groove of the time: the bottom copper 4OZ production line, to compensate for the line, to compensate for the lateral erosion: in the actual production process, we must control the the key process, so as to get good shape, line precise ultra thick copper PCB board.

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