PCB gold finger gold plate quality problems and measures
In the connector plating, due to the contact with a higher electrical performance requirements, gold plating process in the connector plating occupies a significant position now with the exception of some of the tape connector with selective plating gold process, the other large number of needles Hole parts of the hole is still gold-plated plating and vibration plating to carry out.In recent years, the connector to the size of more and more miniaturization, the pinhole parts of the hole quality of gold plating has become increasingly prominent, the user of the gold layer Quality requirements are getting higher and higher, some users of the appearance of the quality of the gold even reached a critical level.In order to ensure the quality of the connector gold-plated layer of these common quality problems are always improve the quality of the key gold-plated connectors. The following reasons for the quality of these issues one by one to provide you with the discussion.
2, gold quality problems arising from the reasons
2.1 gold color is not normal
The color of the gold-plated connector and the normal color of the gold layer is inconsistent, or the same accessory products in different parts of the gold layer color difference, the reason for this problem is:
2.1.1 gold-plated raw material impurities
When adding chemicals into the bath more than the endurance of gold plating liquid impurities will soon affect the color and brightness of the gold layer. If the organic impurities will appear the phenomenon of dark hair and hair, Check the film dark and hair position is not fixed.If the metal impurities interfere with the current density will result in narrow the effective range, the Haier groove test shows that the current density of the test piece is not bright or high-end plating is not bright low-end plated Reflected in the coating is red or even black coating, the hole color changes more obvious.
2.1.1 gold plating current density is too large
Due to the total area of the plating tank is wrongly calculated, its value is larger than the actual surface area, so that the gold plating current is too large, or the amplitude of the vibration plating gold is too small, so that all or part of the groove plating gold plating crystal rough, Stratum red.
2.1.3 Aging gold plating
The use of gold plating solution is too long, excessive accumulation of impurities in the bath is bound to cause the color of the gold layer is not normal.
2.1.4 Hard gold plating alloy content changes
In order to improve the connector’s hardness and wear resistance, gold-plated connectors are generally used hard gold plating process which uses more gold and cobalt alloy and gold-nickel alloy. When the bath of cobalt and nickel content changes will cause The color of the gold coating changes.If the cobalt content in the bath is too high, the color of the gold layer will be reddish; if the nickel content in the bath is too high, the color of the metal will be shallow; if the change in the bath is too large and the same ancillary products Parts are not the same slot gold-plated, so there will be provided to the user the same batch of gold color products are not the same color phenomenon.
2.2 holes plated with gold
When the thickness of the outer surface of the plating reaches or exceeds the specified thickness, the pin hole or the hole of the jack hole is thinly plated or even no gold layer.
2.2.1 plated pieces of mutual docking
In order to ensure that the connector jack in the plug in the use of plug-in has some flexibility in product design, most types of jacks are designed in the mouth of a chipping groove in the electroplating process constantly turning parts The jacks are inserted into each other at the opening to make the power lines of the plug-in parts shield each other and make plating holes difficult.
2.2.2 plated when the end to end plating
Some kinds of connectors whose pins in the design of its needle diameter is slightly smaller than the outer diameter of the hole size of the wire hole in the plating process will be part of the pin will form the end to end contact with the wire hole does not enter the gold plated Both of the above phenomena are more likely to occur during vibration plating.
2.2.3 Blind hole parts concentration greater than the plating process deep plating capacity
Due to the bottom of the slot in the jack is still some distance from the bottom of the hole, this distance objectively formed a blind hole in the same pin and jack hole also has such a blind hole, which is to provide wire bonding When the pore size of these pores is small (often less than 1 mm or even less than 0.5 mm) and the blind hole concentration exceeds the pore diameter bath difficult to flow into the hole, the flow of liquid into the hole is very difficult Outflow, so the hole in the quality of gold is difficult to guarantee.
2.2.4 gold-plated anode area is too small
When the connector is small, relatively speaking, the total surface area of the single-slot plating is relatively large, so if the single-channel plating is more, the original anode area will not be enough when the small-sized pinholes are plated. Especially when the platinum titanium mesh Use too long Platinum loss too much, the effective area of the anode will be reduced, so it will affect the plating ability of deep plating, plating will not enter the hole into the hole.
2.3 poor adhesion of the coating
After plating test connector plating adhesion, sometimes encountered some of the needle pin at the front of the bending or pinhole hole when the flattening of the coating has a peeling phenomenon, and sometimes at high temperatures (2001 hours) test found that the gold layer has a very small bubbling phenomenon.
2.3.1 pre-plating treatment is not complete
For small pinholes, if the machining sequence can not be immediately after the use of trichlorethylene ultrasonic cleaning, then the next conventional plating pre-treatment is difficult to dry the hole in the oil removed net, so that hole plating The combination will be greatly reduced.
2.3.2 substrate activation is incomplete before plating
Various types of copper alloys are widely used in connector base materials. Trace metals such as iron, lead, tin, lead, beryllium, etc. in these copper alloys are difficult to activate in general activation solutions. If they are not activated by the corresponding acid, When these metals are difficult to combine with the coating oxide, thus causing the phenomenon of high temperature foaming coating.
2.2.3 bath concentration is low
In the use of nickel sulfamate nickel plating solution, when the nickel content is lower than the process range, the quality of the small pinhole pieces of the hole to be affected if the gold content of the pre-plating solution is too low, then gold-plated hole There may not be plated within the gold, when the plating into the thick gold plating solution, the holes within the metal layer of the plating layer of the nickel layer has been passivated the result is the hole of the gold layer bonding force is poor.
2.3.4 slender pin plating does not reduce the current density
In the case of plated elongated pins, the tip will have a thicker coating than the needle bar when plated at the usual telecontrol current density, and the tip of the needle may sometimes look like a match-head under a magnifying glass (see Figure 3). The coating of the neck, which is the top of the front pin, is bonded after the gold coating on the back of the front part is unqualified.
2.3.5 Vibration Vibration frequency adjustment is not correct
Vibration plating plating insert, if the vibration frequency adjustment is not correct in nickel plating plating beating too fast, easy to open double nickel has a great influence on the bonding strength.
3, to solve the quality problem
3.1 From the beginning of product design to eliminate the factors that affect the quality of the plating
First of all, when designing the connector, we must take into account the possible impact on the plating process, try to avoid due to improper design to the quality of the electroplating left hidden dangers.
3.1.1 on the shape of the opening of the mouth, the first slot in the groove when the mouth from the mouth edge of the central oblique 45-degree angle to the mouth, and then down the middle of the mouth down vertically if the cross-shaped plug Hole, you can first shut the jack so that the mouth of the split notch width less than the thickness of the jack wall, so that you can reduce and avoid the phenomenon of mutual jack inserted gold plated.
3.1.2 pin design needle pin size should always be slightly larger than the size of the wire hole or hole length to extend the wire hole to avoid plating the first and second pin phase.
3.1.3 At the bottom of the blind hole part of the design of a horizontal through-hole so that the plating bath in the hole smooth access (see Figure 5)
3.2 The use of scientific plating process management methods
3.2.1 to strengthen the quality control of the plating, especially for the quality of the gold salt to be focused on the use of each batch of gold salt in addition to the usual physical and chemical tests have to be taken after the sampling for the Seoul Er tank test, the test after that For the plating tank. Hao Er tank test method: Take the sample of gold salt 12 grams, 100 grams of potassium citrate was added to prepare 1 liter of bath, heated to 50 ℃ adjusted PH5.4-5.8] Hao Er tank test . The normal result is that the bright area of 250 milliliters of the Haier slot test sample should be over half of the area at the lower end of the current density at 0.SA current plating for 1 minute and should be uniform golden yellow on the entire test piece, Golden salt can not be used normally.
3.2.2 The number of plating per slot, surface area, the total amount of current plating before plating calculations and make a record in order to find the cause of the quality problems.
3.2.3 According to the timely analysis of gold plating production adjustment bath, to ensure that the plating bath composition in the best process, nickel-plated solution at least monthly activated carbon treatment. When the use of gold plating solution to more than 70 cycles should be considered to reconstitute a new bath, the old bath after the recovery of gold abandoned.
3.2.4 When there is sufficient anode area for gold plating, a new platinum-titanium anode should be considered when a large number of bubbles often appear on the platinum-titanium mesh used in the electroplating process.
3.2.5 small pinhole pieces before plating add an ultrasonic degreasing cleaning process.
3.2.6 For beryllium bronze connector before plating with a 1: 1 hydrochloric acid solution to boil 10 – 30 minutes, fully remove the oxide and then into the normal electroplating process. For the brass parts should be added before the nickel plating activation solution A certain amount of hydrofluoric acid or hydrofluoric acid with fluoride directly formulated activation solution to ensure that the substrate copper alloy activation of trace metals.
3.3 using advanced plating equipment and advanced plating process plating
3.3.1 After eliminating the unfavorable factors of product design, the quality of gold-plated plating on connectors using vibration plating equipment is obviously stronger than that of barrel plating.
3.3.2 (1) The use of commutation pulse plating power supply for the gold plating power supply, the quality of the deep hole than the DC hole plating quality significantly. (2) In the use of PPR (Periodic Pulse
Peverse) power, the key is the ratio of the size of the positive and negative current, the ratio of the length of time must be selected, otherwise not reflect the best results.
3.3.3 At present, there are many domestic companies to provide patented electroplating process, such as Hippolyte company, Angkolon company and Le Si company’s gold plating process for the quality of the connector plated gold plating more stable. In addition many of our older generation of electroplating work they use their rich experience in electroplating advanced foreign gold-based formulations developed on the basis of some more practical value of the gold plating process. It is recommended that domestic users may wish to use their gold plating process after agreeing to the effect.
In the process of gold-plating, many factors affect the quality of the coating. With the rapid development of China’s electronics industry, some new quality problems will arise. However, as long as we start with all aspects of connector manufacturing, find out the root causes of these problems, adopt scientific management methods for each production process, and adopt advanced plating equipment and techniques as far as possible, these quality problems will be solved.